As my mistress' pet, I often ageplay to feel a little more like her pet - smaller, cuter, more dependent on her - but I also missed out on a very fulfilling childhood, so that may have something to do with it, too.
I've found that, as I've spent time with her, I've gone from genuinely thinking of myself as a child to thinking of myself as closer to my real age. I guess you could say I've grown up inside. <3 So then, I think that the above quote could definitely be an aspect of it.
Granted, I still like to ageplay just for the sake of feeling cuter!. ^.~