This is straight from mystery method, but i think it's really true.
I am also 21. and once you realize that being young is a GOOD thing (well.. maybe 18+) than you can frame it as a neg if it ever comes up
HB: Ahh!.. but you're soooo young
PUA: yeah.. i noticed.. poor you!
or
HB: Ahh!.. but you're soooo young!
PUA: haha.. okay.. i'll give you a second to get over this whole "age" thing
or even
HB: Ahh!.. but you're soooo young!
PUA: Yeah.. I know.. Tragic.. In 10 years i'd be forced to dump you and get a younger hotter version of you!
Never apologize for your age..
I wanna be 21 forever.. lets be real! Haha