How to convince my rents i am responsible enough to live on my own?

Ok so basically i moved out of my rents house fri last week....but i don't think they knew i was serious about living on my own. So i'm living with my 3 good friends in a house. But basically my rents think i am too young...i'm 18... i have a job working part time as a computer tech at school pays 14.75/hour which is good, the rents is low cause it's my friends rents other house....their loaded... but the point is it's free rent...all we have to pay is utilities and food but w.e it's easy for 4 ppl to pay it. it's 4 bedrooms so we all get one..... my gf is kewl with me living with 2 females...but why are my rents so overbearing on me...??? it's not like i'm irresponsible or anytihng.