As far as aging/how old: give it up. There is no internally consistent logic on how Marvel characters age.
That some what true but, when the FF debut in story is supposed to be the don of modern super heroes & the are modern teams (with them being 1st team).. So marvel for the most part doesn't let super heroes age or be active long than the FF have been a team.. The FF have been active in story for about 11-13 years (If I remembering correctly it was Slott or Joe Q said this or it was both).. So Storm can never be X-Men long than 10-12 in story & Kitty can never get to say 25 that is until they change the # of years the FF been active/started there team.
That's true, but if Kitty is in her early to mid 20s, Storm has to be in her early 30s. We've seen Kitty drinking beer, so she's 21 at the very least. It's impossible to guess age, but it's rare for some characters to age and others don't (except kids).
True, I think Kitty is 21 maybe 22 at the most, I don't think it impossible to guess age to guess age hard/very hard some time yes but not impossible imo.. Kitty join the x-men like 1 or 2 years
marvel time with the slowed time scale (1975 to 1980) after Strom did & they both been with the X-Men for about 7-10 years imo.. I think Storm was 18-20 when she join (but I could be wrong) which mean now she at least 29/30 & Kitty was 13/14 when he join.. so her being 21 make works..
Also it I agree about it being rare, Kitty, Jubes, Cannonball Moonstar, Cloak, & the other characters in there early 20s/late teens are the last generation of super heroes in marvel that can/will age some what..
Will be all be very old or long dead before Marvel will let (if at all) Franklin get 20 (he's like 9/11 now but he should be more like 15)..