I tend to have a similar 'problem' in that I've always gotten on better with older people. I do believe that being an only child doesn't help - and as I never went to school close to home, I grew up spending much more time with older people (my parents, their friends) than kids my own age, since there were never any I knew in walking/cycling distance.
I can't say I've ever been called 'cute' before though o_O... my point is that, if you are an only child, that's probably a factor. Also you may be mature for your age (as a cause or an effect... I've been told I dress and act like I'm 30 -_-; ).