I'm 33, and hearing music I listened to while I was in high school on the oldies station (K-Earth 101 where I am) makes ME feel old! Otherwise, nope, I still feel young. I still laugh at burps, farts and ketchup or shampoo bottles that make fart noises. I'm so immature, but I don't care, so nyaaaah!
Right now, I see kids who were born after 9/11 who don't know a thing about it and I just want to smack their teachers and go "these young ones are the future, they should know what happened in their recent history to be prepared in case it happens again!"
Something else that makes me see kids as really young are kids who were born around 1990 or later(I was born in 1980.) I remember watching Talia Joy Castellano's makeup tutorials and admiring how cute and young she was. Far too young to die of cancer like she did. She did her makeup, but she never tried to act older than her actual age. She was always so happy and bubbly.
I generally say people aren't old until they start feeling their age. IE arthritis, health problems, etc. My dad is 65, but sometimes I look at him like he's 80 because he has Parkinson's and it's advancing really fast on him now. He moves like a really old guy. Then you've got my mom, who is almost 70, and sometimes you'd swear she's only 40 with how she's still active. She does have health problems of her own, but they're so invisible that if you didn't know she had them, you'd never know by looking that she's got them.
I think it's sad how kids want to grow up so fast. I see 12 year olds bragging about having sex and I want to scream. When I was 12, I was still doing kiddy things like playing with my mermaid Barbie and pretending to be a mermaid in the huge wading pool all the neighborhood kids liked to play in. (I was so sad when the family who owned it moved away!)
Age is just a number. When I look at it that way, I don't really think someone is young or old based on them saying "I'm 89!" or "I'm 11!" But I might think someone is old if they were old enough to remember where they were when JFK was assassinated.
My grandma was 81 when she passed away in 1995. The first president she could remember was Woodrow Wilson.
Now compare that to me, at 33 right now, and the first president I can consciously remember was Ronald Reagan.
Oh God, I'm sorry if that was rambly and senseless.