When I had to have organs removed and body parts repaired.

Gray pubes were the beginning.

When some smart ass teenager called me "gramps"

I'm still trying to figure out how that grey haired guy got in the mirror! And I'm only 64!!

When half the worlds rock stars keep dying and I'm thinking 'They were how old?'

About 5 years ago, paddling out against a surf with teh young guys and I couldn't keep up. Has gotten worse since.

If the secret is "weekend out"....dear, I am a teenager; I go out every day.

I haven't yet..so tell me what's it all about?

When my knee started hurting before major thunderstorms. And my Gibson ES-175 keeps getting heavier....

I'll add something to an earlier answer. I resist the idea that I'm getting old but it is getting increasingly difficult when my 11 year old groups dinosaurs, the stone age and me and being around at the same time.......Love you

When it took two days to recover from a hangover. ?

I never really liked going out lol

When I got my knee replaced.

Most days I haven't gotten there yet. Maybe when I'm 70 I'll think I'm old.

If you think your too old then you are.

When I could no longer have sex twice in quick succession!

When I was admiring the skills of cute little middle schoolers in a marching band parade, then realized they were university students. Ooops.

I remember listening to "Lunchtime with the oldies" on the radio while I was at Ft. Meade, Maryland. I was in my early 20s, and they played a song that I loved in high school. I was pissed about that for days! And that was the first time I realized it was really all downhill from there. My middle daughter freaks out about wrinkles and turning 30! I told her "really? Every wrinkle and grey hair I have has your name on it" I may be old, but I don't care! I'm OK with it. My mom died at 45, she never got to meet her grandchildren or see any of her kids get married or any of that other cool "getting old" stuff. Your age is just a reflection of the number of trips around the sun your have made. Don't let your age define you. I may be 60 and my knees make some odd noises and yes I have a few gray hairs but dammit, I put the time in for it. I earned it! I am happy about it because so many don't get that opportunity. JMHO ( or not so H)

When my friends started making babies on purpose.

As I read your question it occurred to me.

Oh shit! I am old.

Thanks for that.

When hair started growing out of my ears

when i did the pogo for 2 hours and couldn't walk properly the next week [ last week after orchestral manuvers in the dark]

When I went out and tried to pick up a 20ish young woman and she give me the look plus a EeWW! ?

I realized it when I walked passed a cemetery and two guys started chasing me with shovels.

Old? I still think I am a kid, though my body and some othe prople point out otherwise. I have a 9 year old daughter who is too often mistaken as my grand daughter. I was at the park with her and another parent with her kids and additedly she looks young next to me. But another little kid asked is she could play, being a parent she tried to decline and the kid said "you could ask your dad, pointing at me"
THAT is when I realized I was old.