Some abbreviated replies from an interesting thread at Reddit -
Minor accidents like falling down hurt considerably worse and for longer.
I had to specifically ask for socks last year and I was legitimately excited to get them.
The first time I had a doctor younger than I was.
Someone mentions being born in the 90s.
When I started getting tired of all the bullshit. ALL of it. Then I realized I had become the grumpy old man.
When I realised I'd started checking for wedding rings.
My friends and I were talking about the price of toilet paper tonight at the bar.
When the flashback weekend on the radio station plays the stuff you like.
When your friends start having babies that aren't accidents.
Here's my offering. When I lived in Kentucky in the 1980s, my friend's daughter came to him with a question. "Daddy, settle an argument. Didn't Paul McCartney have another group before Wings?"
When did you first feel "old" ?