I really like Caitlin, and I wish it had not become so crazily popular and washed out by all the variant spellings. I think the youngest Caitlin I know is around 7 or 8, and there are a half-dozen older Caitlins at my church. I'm not sure about spellings, but I think the most common choices are Kaitlin and Katelyn.
Caitlin is really the only spelling I like and the only one I would consider using. I'm so used to Kaitlin, Kaitlyn, and Katelyn that they don't bother me. Catelyn is interesting, too.
If you add up all the different spellings, it's still a popular choice today.