Well, consider a possibility: Might you be comparing yourself to the person you were in school?
25 would be old for a 14 year old. 25 would be old for a 19 year old. But 25 would be young for a 30 year old. 25 would be young for a 40 year old.
25 is just right for a 25 year old.
Here’s me in 1983 when I got my first computer. Got online in 1989. Best thing ever. I’m still that kid.. .and at 44, I’m also the person he wanted to be. At 24, I had severe doubts. Time passes either way.
I think the kernels of your future hide in the present. Retracing my “life so far” (with STILL no knowledge of the future), the connections are pretty cool. I look at paths-not-taken and in my mind, they’re just taken by someone else. When I see someone living a life I could have, I’m glad – it’s like they’re working for me. Or, in some alt.fictional.universe, there’s another me doing that path instead. Freed me up from having to do it.
Maybe that’s what’s making you feel old. It’s like an old pair of shoes that used to fit you. Now they don’t fit anymore. Your feet have grown.