That's a good point. BtVS is the only comic I've ever read, but I supposed it'd kind of like how people stay the same in cartoons. The Simpsons kids have been the same age for over 20 years. The South Park kids have only aged a year in about 15 (I think). Also, any personal growth a character might have is ignored in the next episode. I suppose it's much harder to keep age and maturity stagnant when you have actors who visibly age, etc. However, the lack of character growth in the comic book medium is much more frustrating than usual since Buffy started as a TV show.