I often think that people misconstrue (like with many other things and terms these days) what it means to be "immature". Simply collecting collectibles, taking an interest in and enjoying the same things that you enjoyed during your youth, does not make one "immature". As if at a certain age, one is supposed to start from scratch and acquire an entirely new set of interests and likes and forget anything they ever liked in the past.
I've always maintained the conviction that while of course one should grow-up mentally; be responsible, be courteous and respectful to others, speak intelligently, possess integrity, etc., you should never let die (the inner child) what makes you, you. You shouldn't ever have to apologize for, require approval, or be patted on the hand so to speak and be told it's ok to like what you like (given that it is harmless and doesn't degrade nor harm others).