Some people have a higher level of tolerance for fanciful things. I have a friend who is older than me who likes dressing up for Comicon, and I know people much younger who would just find that completely stupid.

I will say, though, that the people who still live with their parents in their 20s and 30s and don't want to face the real world are more likely to regress into infantile things, so maybe there is a component of "facing reality", which comes with age, coming into play in the equation, but even so, a lot of it varies from person to person.