Haha.

As with everything, it totally depends on the person. I've known guys who were what I would consider grown up at 25 or 26. Of course, my definition of "grown up" still allows for trips to the ice cream truck and nights out drinking, so maybe I'm not qualified to speak on the matter. ;)

It's best to achieve a balance between being responsible and still having fun.

Trips to the ice cream truck are ageless! If you can ambulate, you can do that!