My mother is the second oldest in her family. Her older sister’s first born is 1 year older than their youngest brother. They went to the same school and T. took great pleasure in calling him Uncle Bob. I am 2 years younger than Uncle Bob.
T’s daughter and my son were born just a few days apart and are again older than Uncle Bob’s three kids but it’s less intersting as the relationships get further apart 
I suspect that as family sizes continue to shrink this will become even less common.
As the result of my great-great-grandfathers second marriage, I had an uncle who was a couple of years older than his great-aunt. I guess technically, it was something like a “half great-aunt.”
I guess it depends on how you define “knowing”. I met my great-great-grandmother once, in India, when I was six. She was about 112, although nobody was quite certain because she had no birth certificate and nobody else remembered.
She was pretty immobile; she sat on a straw mat all day and was fed by others. She didn’t speak. Couldn’t, in fact. Didn’t appear to understand who I was, although I got the impression she recognized my mother.
However, she bathed herself every morning, without any assistance.
One lady in my (married into) family is 93. Let’s see if I can back-calculate… She had her second child at 23; that daughter had a second son at 26, whose first daughter is now 18… fortunately no children, but based on timing the lady could have been a great-grandmother by now. Her eldest grandchild is over 40 and her youngest is 16.
I suppose it does require that nobody wait too long; at 20 years old, and assuming you need to be about 5 to remember someone into adulthood - a child at 20 means
85yo gggm, 65yo ggm, 45yogm, 25yom, and 5yo child. Not preposterous or outrageous. Just, in today’s climate, rare.
I worked with a lady who was a gradmother at 35; her daughter had thoughtfully waited until she was 18, unlike this lady and her (now) ex-husband. However, both grandchildren are about 18, 20 now and no offspring that I know of yet.
That’s the thing. Unless it’s a major oops and the person is unwilling to consider abortion, children arrive much later than 30 or 100 years ago. Modern society is structured around 2 people working to support a household in moderate luxury, so the financial burden of a child is usually put off as long as possible.
In high school I knew a girl who was born to a 14-year-old mother, who was herself born to a 14-year-old grandmother. Guess how old she was when she told me this, and what my first question was. 
Probably uncommon. I had a g-g-grandmother alive when I was born, plus four g-grandparents. I don’t remember my g-g-grandmother, she and my g-grandfather died before I was 5, but one g-grandmother died when I was in college and the last just after I finished.
I too get those same looks of disbelief from people when I say I knew my Grandpa’s Grandpa (My Great-Great Grandpa) and my Grandma’s Grandma (My Great-Great Grandma).
I was 6 years old when my G-G Grandpa passed away (he was in his 90s) and I was 15 when my G-G Grandma passed away (she was 105)
And I have an older brother who was 18 when my G-G Grandma was alive so we very easily could have had 6 generations.
The two key things here in my family anyway is 1. my G-G Grandma lived an exceptionally long life and 2. each generation was the first born in their families, my mom was the first born, her mom and dad were the first born as were their moms and dads and their grandmas and grandpas and not one of them was 13 yrs old when they had their first kid. on my G-G Grandma’s side the ages were…
Me 15, Mom 35, GMa 55, G-GMa 80, and G-G GMa 105.
And my G-G Grandpa’s side…
Me 6, Mom 26, GPa 45, G-GPa 70, G-G-GPa 93.
Now my younger brothers (6 and 7 years younger) didn’t know our G-G Grandpa so the chain is easily broken in just a few short years.
But they do remember my G-G Grandma because she lived so long.
My uncles wife had 8 grandmas alive when she was born.
Here is an article that was written in the local paper when she was 2yrs old.
Need Not Worry
Over Any Lack
Of Grandmothers
Little Sharon Kay . ., 21
months old, has no need to worry
about grandmothers, great grand-
mothers or great, great grand
Mothers. She has eight of them
All together. The two great great
grandmothers are Mrs. Mary . .,
and Mrs. Mary. . The
four great grandmothers are Mrs.
Lizzie…, Mrs Cloie…,
Mrs. Minnie…, and
Mrs. Lillie…, the t w o
grandmothers are Mrs. Ida…,
and Mrs. Lucy…
One other point to show how easily the chain is broken…
None of my mom’s sibling’s children knew my G-G Gpa just because of a few years or even months difference.
My mom’s brother (2nd oldest and only 2 1/2 years younger than my mom) barely missed having 5 generations in his line by a month or two because his son was born a month or two after my G-G Gpa passed away.
Uncle’s son (new born), Uncle 23, GPa 45, G GPa 70, G-G GPa 93 –(Dead)
I think all 8 of my great-grandparents were dead when I was born. I think.
My parents were 34 and 35 then and they were both the youngest siblings in their families. My youngest grandparent was 60.
Based on what my parents have told me, my G-Grandparents would have had to been somewhere from their mid 70’s to 90’s for them to have known me as an infant. None of them made it of course. That’s on my adoptive side: if I had found my birth mother earlier I could have known my maternal birth G-Grandmother, who lived to be 95, when I was in my 20’s.
When my maternal grandmother died she was 92 and had 20 grandchildren and almost 30 great-grand children, the oldest of which were ready to start college. No Great-greats though.
When I was in the hospital 2 years ago the guy in my room was a 90 year old stroke victim who was in otherwise good shape. He told me that he lived in a house owned by his great-grandson, he also had one 3 year old great-great grandchild. He was a little upset that since his stroke he’d have to live with his elderly son.
(This guy was a WWII Navy veteran named Bill Reynolds, Pittsburgh Dopers may know him from WQED’s “Cemetary Special” he’s the old guy who helped find the graves of Civil War soldiers. He was Bloomfield’s “Man of the Year” in 2008).
My last great-grandmother was 102 when she died, in 2003. I was the oldest of the great-grandchildren, at 27, and really we all could easily have had kids going just by the calendar (only four of us, but we were all in our 20s)…if I’d had a kid at 21, as my mom was when I was born, they’d have had a reasonable chance of at least a faint memory of Grandmother – I should hope so, the woman was a force of nature and her picture should be next to the word matriarch in the dictionary. I miss her.
I suspect it’s uncommon but entirely possible. I kind of wish one of us had been in a position to make her a great-great while she was alive, she’d have loved it.
My grandmother died at the age of 93 a great-great grandmother. Her daughter, my aunt was married in her 20’s, her son (my cousin) knocked up his high school sweetheart (now divorced) and then their eldest son had a kid in his early 20’s. (My grandmother is the great grandmother of the field goal kicker for Iowa State.)
Several years ago, a tabloid, maybe the National Enquirer went out to find the youngest grandmother, and their winner was 28 years old. Here are some other general answers to the question of youngest grandparent:
The oddest family relationship were these two guys with the Uncle being 10 years younger than the Nephew. Probably made for some interesting family discussions. I can see a little kid trying to boss around a teen and tell him that he is his uncle, with the teen getting tired of the bullshit and twists his arm around saying “Say Uncle now, bitch!” Or not. Families would never do that.
I’m closer to this as well. My great-grandparents were all dead by the time I was born, forget my g-g-grandparents. My family is pretty nomadic and spread out, so it’s hard for me to be sure about the details, but I think my g-g-grandparents were all born in and around the mid-19th century. It would be highly unlikely any of them could have been around by the time I was born in 1978. Especially on my dad’s side, since it was their children’s generation that immigrated to the US, so they would have still been in Eastern Europe in the 1930s and 40s, and it’s unlikely they would have survived WWII. (My bubbe claims none of our relations were killed in the Holocaust, though, so presumably they were deceased before then. My dad thinks my bubbe has no way of knowing for sure and is delusional.)
The 2000 Census listed just under 100,000 centenarians in the U.S… Today would be a completely different batch of centenarians (give or take about five or six or so) but it’s probably a similar number. Since a centenarian can easily have great-great-grandchildren it’s probably more common than ever before, but I doubt anybody grows up with clear memories of their g-g-grandparents.
On the other hand, an interesting thing about centenarian women is that the percentage who had their first child after the age of 35 is about 3 times the percentage of a random group of women, while the percentage of centenarians who had their first child when they were teenagers is about half the percentage of a randomly selected group of women, so it stands to reason many centenarian women do not have great-great-grandchildren.
Fewer than 1% of the population has a full set of great-grandparents alive when they’re born, though most have at least one.
There have been women who lived to be great-great-great grandmothers. Here’s a recent one in San Antonio (she’s 107).
In a hypothetical family in which every firstborn is a healthy female who gives birth at the age of 15, a great-great-great-great-great-great-grandmother is theoretically possible, though she would be 120 years old. This makes me wonder what the record is- has anybody ever become a quadruple great for instance.
I’m 43 and all 16 of my great-great-grandparents were adults during the Civil War, which is probably more common than somebody my age who could remember any of their g-g-grandparents.
On the other end of the spectrum, John Tyler, the 9th President of the United States has two living grandsons. John Tyler was born in 1790 and died in 1862. He had a son when he was 63, and that son had two sons when he was elderly with an obviously younger woman.
I don’t know this, but it is very possible that my grandmother was held as a baby by people who fought in the Civil War and even knew of life before that time. There is a picture in my father’s house of my grandmother’s parents, which was taken, I would say around 1900-1910 by the style of clothing and the professionalism of the photograph. So their parents would have been definitely people born and likely died in the 19th Century.
I have very clear memories of my g-g-gandma, as I said in my earlier post I was 15 yrs old and my brother was 18 when she passed at 105 yrs old and we both remember her very clearly.
I even have a few clear memories of my g-g-grandpa even though he died when I was six. Even though there are only a couple of these memories of him, I remember them very clearly because they both had some significance about them that I will never forget. (they were both good things
There was an guy in his 80s that died in a car wreck in my community. This would have been around 1998. Turns out his FATHER fought at the Battle of Gettysburg! That astounded me.
Fascinating… Is there any evidence for why this is so? Off the top of my head, I can come up with behavioral or hormonal explanations, with the causality going either way, as well as the possibility that it’s due to poor records 90 years ago.
I can only recall meeting one of my great-grandparents. I was 4 years old at the time. She died 18 months or 2 years later.
It’s possible that there were some other great-grandparents alive when I was born who I never met. Or alternately that I met but don’t recall meeting because I was too young.
I certainly never met one of my great-great-grandparents.
I think meeting a great great grandparent is rare but not unheard of. It would be even rarer to remember a great great grandparent. Since there’s a good chance that ancestor would die before you’re old enough to remember them.
Whoopi Goldberg became a great grandmother at 58. If her great grandchild has a baby at 18 then she’d be a great great grandmother at 76. If that great great grandchild had a baby at 18, Goldberg would be a great great great grandmother (forget about great great grandmother) at 96.