I've actually always been told , "You're too mature and want to grow up too fast," and, "Enjoy your childhood while it lasts," when I really want to become an adult. I think that there are two sides, being immature and being way mature. I guess both are OKAY, but some people take a bit far at times, others can be rude about it. It's a tough subject, yet it seems simple.
In short, I think you should do whatever makes you happy. I understand peer pressure (social anxiety here), but sometimes you just have to stop going with the flow and go with your gut.
Thanks for reading!
Oh, here's a bonus cookie, too: