Anxiety over looking so young...,

I know people will think it is not an issue and that I should be happy I look so young but it is ruining my life. I am 29 soon and people still put me as 16-18, never more then 20 years old. I have a young face, flatchested, quite small in height and very slim so I guess that doesn't help. I work in childcare supervising my own daycare and most of the parents still assume I am a teenager which I find weird given my role but I guess people don't think.
My first question is, should I go and see a doctor? I worry that I am underdeveloped and that it isn't right to still look so young at nearly 30.
My second question would be, what would you think of a woman who was almost 30 but looked 16? Would you assume there was a problem?
I guess I feel people only like me as they think I am a very young girl. People mother me and speak to me like I am a child. The absolute shouts of amazement when people find out my age is so humilating so is being asked if my 16 year old sister is my twin. I am worried now my 29th birthday is approaching as if people find out wt work they will go on about it for ages and each year that passes makes me feel even more of a freak for looking so young.