How to grow up and act my age? *I am serious*?

Well honestly you dont sound all that bad when it comes to being childish but if you want to act your own age then just stop doing the things you know are for little kids. now this is just my guess but is it possible that you are afraid that those years are behind you and you dont want to face whats ahead? is so then you just need to its apart of growing up, you just have to take it all one day at a time and granted it seems scary at first but you'll be ok. put another thing is just cause your 18 doesnt mean you cant have fun, its just a bit creepy that you do some of those things frequently. and im not bashing you or anything i know older people who still goof around every once in a while and go in the ball pit and stuff so i say maybe just dont do it as much and eventually you may not want to do it anymore.