Yeah when X-Force was still going on I think that much of the team was in their early to mid 20's, except for Tabitha who was younger, and as for M I think that she was probably 18 or more by the end of Gen X so no they did not go from teens to adults together, Terry is like four years older than M or something like that, and I'd question whether they were each others best friend as well, not sure who is though...
And while the X-Factor book may have lasted ten years if that, it only lasted like a year or two in the comics...