I'm terrified of growing up?

So I'm a 15 year old boy. I've never liked birthdays because I look young for my age so I don't want to be even older looking even younger and I'm just terrified of turning 16 (which I will this September) because I'm kind of still a child you know I don't feel 15 I feel like I´m 12 or something sometimes younger and I'm scared of growing up and not being able to be a kid anymore and having to have responsibilities and be grown up and not being able to depend so much on my mother and I'm not that scared of being in my 30's or so ... I'm more scared of being 16 onward until like 20 or 21 or something like that ... It freaks me out anyway i just want to know if this is normal if anyone feels the same way as me and any advice or something like that...