I'll be totally honest, most of my characters don't have a defined age (as they're dragons/demons/etc.) but in terms of... character "mentality" (I guess? Like the age they act like/appear as), most of my characters are in the 25-45 age range, give or take.
I've never really cared for underage characters (nothing personal, truly- I just honestly am not a fan of kids IRL, and when it comes to my roleplaying and writing, I've always touched on mature themes in one way or another so I haven't really had a use for them?)- so even when I was much younger, the characters I played were always adults.
I actually usually lean towards older characters (with a max of about 50, give or take) and always have!