He’s 30, I’m 25. He’s been married to my niece (who’s 26 and was in the same grade as me) for 6 years. My great-nephew’s birthday party was today; he turned 3. My nephew was very confused as to why I signed his card “Great-Uncle Alphaboi” when I was his (the birthday boy’s) uncle. I corrected him and pointed out that I was his uncle. He looked very confused and said he thought I was my his wife’s cousin (which we did tell people in school, but that before they met). His realitives also seemed confused, our side (including my neice, his wife) thought it was hysterical. It all goes with the territory of being the product of a second marriage and freakishly younger than your siblings.
If it helps any, I’m confused too.
It’s simple. Alphaboi has a sibling (perhaps a half-sibling) who is much older than he is. That sibling had a child. Then Alphaboi’s parent (or parents) had him. So he is younger than his niece, and she is older than her uncle.
So his niece got married and had a child who is now 3. But his niece’s husband thought he was his niece’s cousin, not her uncle. And so the “Great Uncle Alpha” on the card confused him.
Alphaboi, we have this same kind of situation in my family. My husband had some trouble getting used to the idea of having a BIL who was about the same age as his (husband’s) father.
It’s a fun, and funny, sort of thing to play with.
My dad remembers playing with the younger members of his family - he would have been 10 and ‘looking after’ the little kids all around five years old.
Kid 1 said;“Pass me the ball, Kid 2!”
Kid 2 (dad’s little sister) drew herself up and spoke in icy tones;“That’s Aunty Kid 2, to you!”
Almost 60 years later, dad still tries to tease her about it and she still insists that she was right dammit.
We have the same sort of situation in my family–my mother’s youngest sister is the same age as my older brother, both about 2 years older than I am. When we went to visit Grandma’s, our younger aunts and uncles were our playmates.
Now, I have first cousins 25-30 years younger than I am, around the same ages as my brothers’ and sister’s kids.
My son is around the same age as my 5 half brothers/sisters. He’s older than his three aunts.
This sounds like one of those weird logic puzzles.
Three years ago I was half the age of my niece, now I’m four times the age of my great nephew. How old am I?
I have a nephew a year younger than me (their parents married 5 months after I was born), this is mainly due to my wife being older than me, and being the baby of the family (her oldest brother is nearly my parents’ age) - of course the nephew (oldest son of wife’s oldest brother) is not related by blood at all either. I insist he call me “Unky Dave” even though we’re both in our late 30s. 
I also became a great uncle the day after we married, again thanks to wife’s oldest brother. This time, her oldest brother’s youngest son (who was 17 when we got married) impregnated his girlfriend and she was due to give birth around our wedding. Said nephew’s GF was rightfully pissed when not only did he go to our wedding while she was in the hospital (he was an usher), but he went to the lake to go fishing with his brothers after our wedding (the day she gave birth). (Coincidentally, the day my wife and I met was nine months to the day before we got married (we met at a party on a Friday night). I guess we weren’t the only ones having a good time that weekend!)
Nephew is more mature now and he and GF are married with two kids. But I always tell people that the only reason I’m a great uncle is that I married a great aunt (hey, it’s her nephew!)
My little brother (technically a half-brother) was born when I was 21 and our older sisters were 23 and 25. he’s been an uncle for most of his life.
I wish.