Yeah, I always tend to go by more of a vague idea about how old they all are based less on a number and more on "stage of life." And let's face it, once they get past 20 they pretty much all have a window of ages they can be. I think most people just go by the age the character seems based on whatever factors they pick up on, and keeping them relative to each other. Like I know somebody at one point said Bruce started at 19, which I just can't see. Batman has never been a teengager to me. It just wouldn't have worked, even with Bruce. Babs is older than Dick, who's older than Jason, who's older than Tim...but the Robins have gotten closer to each other in age to each other over the years. Kind of a sliding scale to give everybody a spot.