I've been thinking about this alot as well...
You can look at it two different ways...growing up and growing out.
By 'growing up' what I mean is, taking on more responsibilities. Doing things for yourself and standing on your own two feet. Taking care of loved ones, bills, work, everything of that sort.
By 'growing out' I mean giving up everything that would deem you childish or juvenile in the eyes of others...like visiting this forum for example.
Now based on that...DON'T grow out. You'll become a narrow-minded and obnoxious f**kface if you do.
These are the people that think you're immature for liking comics and certain movies and so on and so forth.
And if 'growing up' the way those kind of people would tell you means becoming a boring and heinously uninteresting ass...no f**kin' thanks, I'll never grow up that way.
You can be responsible and mature without giving up your passions.
In fact there's a theory I have...that I may have discovered the fountainof youth.
BC I'm 19, but I could physically pass for 15 I'm not kidding.
And I think it's because, unlike my peers in high school who traded in the likes of Batman and Superman for Rap and Booze (not bad things mind you but still...), I didn't give it up.
19 years old and I still love comics and action figures and super heroes and science fiction movies and everything that pertains to being a "fanboy" and as a result of hanging onto my childhood passions and interests it's kept me physically young and looking younger than I am...but not mentally.
If anything, being a comic book/sci fi movie/horror movie geek gives me a much broader sense of the world around me...in turn making me more knowledgable and thusly more mature than those who thought growing up meant giving up what they loved as kids.
Bottom Line:
"Growing Up" and "Growing Out" are two different things. They don't go hand in hand...so don't let anyone tell you different.
CFE
p.s. as far as "growing up" is concerned...you're already 19 and asking this question? Yeah kid gloves are off, man...you should definately be more responsible and mature by now. At least you were responsible enough to ask for advice about this rather than not "grow up" at all...so kudos