The first time a cashier calls you ma’am or sir.
The first time you grunt getting out of a car.
The first time you have to push off the arms to rise from a chair.
Others?
First time you get carded for cigs/alcohol.
Joe
First time you hold something further away from your face in order to get it in focus.
First time your doctor is younger than you.
When you see teenagers wearing something that YOU wore back when you were a teenager.
When you don’t know any of the music on the Top 10 lists.
First time you don’t get carded for cigs or alcohol.
First time you get pulled over by a cop who doesn’t look like he’s old enough to drive.
When you go to a reunion, and find it full of grey haired (or balding) old buffers, and they are your contemporaries.
Grey pubic hair.
You buy cereal for the fibre content.
Sucking in the gut doesn’t do anything.
Someone gets up and offers you their seat in the bus/tram/metro.
-Tcat
When the first year students at university don’t look any younger than they did in previous years.
When the music of your youth is on at the supermarket. Or worse, when your music is on the oldies’ station.
When you recall the last time a particular form of nostalgia was in fashion.
The first time your barber briefly directs the trimmer inside your ears.
It starts to rain and you think “that’ll be good for the garden”.
You realize you and your friends have been discussing retirement plans for the last 30 minutes.
You haven’t closed down a bar in years.
You get carded and hand them an AARP card and ask for a discount.
About eight or 10 years ago, I started noticing that professional athletes (baseball pitchers, football quarterbacks) were starting to be younger than me. That took some getting used to – I grew up watching them on television, and they’d always been older than me.
legally being able to buy alcohol.
I used to buy alcohol every weekend before I was 21 from older friends. Now I’m 28 and sometimes I feel like I’m doing something bad. Also I’ve recently stopped being carded for the alcohol, but I got a big ol’ bushy beard now so that probably helps.
The first time you see some 20-ish hottie sitting & yakking with a woman obviously her mother …
and you think about hitting on the mother.
This one was a real one for me last week:
Going to your first child’s information session for Kindergarten for the upcoming year. I think the key was that you don’t often get to be in a room with a bunch of people roughly your age after you leave your early 20’s. It is even weirder when they are acting all parentee and enthusiastic to ask the really responsible adult questions. It was the first time I felt like a real, honest to God, parent even though the kids have been in daycare that wasn’t much different since they were tiny.
The first time you receive and throw out the AARP application.
When all your kids are gone. (Not all these milestones are bad 
)
When your father, whom you’ve always looked up to as all-knowing and generally superhuman in every way, gives you his car keys and says he’s not comfortable driving that mountain road to the family reunion.
Also car-related: when you finally buy a car with an automatic transmission.
I thought there was a surgical procedure to remove milestones now.
Getting carded for tobacco or alcohol and secretly being pleased because it means you still look young. (Except at places that have a policy of carding everyone.)
Getting a pimple and secretly being pleased.
Hearing “Sir?” or “Mr. Spoons?” and realizing the speaker is not addressing your father.
Realizing that you start many sentences with “Years ago,” or “When I was young,” or “In the old days.”
Seriously considering travelling first class.
The first time I picked up my mom somewhere and I was the driver and she was the passenger really made me feel like an adult, and was really, really weird, too.
The first time I bought myself a new car without even considering asking either of my parents for their opinion made me realize how adult I had become.
The first time I had a job that included a security badge and password made me feel pretty adult, although I think high school students might have them nowadays.
And buying a house, of course, was almost stunning. The biggest check I ever wrote by about a factor of ten was my the check for my downpayment.
Then there was the time that I found out a coworker, a mother of two and really awesome professional, was born in the same Chinese year as me, except 12 years later.
I had one tonight –
When you see tampons on sale, and you not only don’t stock up, you don’t buy a single box – because there’s a full box at home and an almost full box at work, and who knows, that really could be enough to get you through whatever menstrual stuff remains.
Death