[Nyororin]

I think that you`ve mistaken "immaturity" for "individuality". They are not quite the same things. Someone can still hold on to their dreams, and continue to do things they enjoyed as a child - but be mature at the same time.
Maturity isn`t about conforming, but about having the ability not to screw yourself over.

Maturity is realizing that it may be great to build stuff with Legos, but that they cost money so some time must be dedicated to living so that you can comfortably support your Lego fun.
Immaturity would be thinking that someone should support you because all you feel like doing is playing with Legos day in and day out... And likely being offended when someone points out that such a line of thinking is immature and tells you to get a job.