Please, i need some support?

Im turning 26 in march, and i cant stop fixating on the fact that i grew up! or did i? i mean when i turned 23, i thought i grew up...of course i was wrong...then at 24 i made a pact with myself. Dont think about it! Youre very young and take care of yourself until you are trully old! And again then, keep up the excercise and healthy life style! So when i hit 25, i said who cares... But now i feel old again! Am i old? i believe i have years in front of me before settleing down! I like sports, having fun getting wasted and not having a steady girlfriend! But then come the depressive thoughts! I feel like an old man esp in front of teenagers! But i see people in their 30's and they look young and energetic...i am not even close 30 and i feel depressed, old and EXTREMELY pessimistic about life! I neen some words of comfort PLEASE! I m starting to lose it. i Am male btw