Miles lays it down around here!!
While I agree with Carl that you dont have to be "grown up" you just have to have everything OKed with your parents first.
Im only 21 so I guess Im grown up but in alot a ways not so heres what I will tell all the 16 year olds out there. LIVING AT HOME AINT BAD!!! Life is expensive and enjoy it while you can. Some one here said its MY room therfor my parents shouldnt come in. What kind of bull **** is that?! Did you buy that room? Do you pay the electric bills? Who feeds you? What about your car and who got you to and from school/work/sports when you didnt drive?
Baisically I was the same way when I was that age. But honestly your parents are doing SO much for you its hard to imagine untill you do it on your own. If it means you cant add that bajillion tank in their house so be it. Be thankful you are fed and have a roof over your head. When you do get out on your own and IF you have the space and money by all means go for it, but meanwhile understand where your parents are coming from and by God respect them!!!