I'll be 18 next month, but people always mistake me for a 12-year-old.

Example:
My dad, brother, boyfriend, and I went to the wrecking yard the other day to find parts for my old truck I just recently bought and am restoring.
The guy at the front desk looked at me, then my dad and said "17 and up only."
My dad said o.k. then continued to the door that leads to the cars.
The guy stopped me and said "17 and up only. Sorry, but it's for insurance purposes"
I told him that I am 17, but he didn't believe me so I had to show him my license.


Example:
I went to Six Flags about a month ago and played the game where the guy guesses your age.
He guessed 12 and when I said I'm 17, he didn't believe me, and actually got mad.
He said "I can't prove that you're not 17, so I have to give you a prize. You should try being honest with people from now on."
I had to show him my license.

Example:
A guy was going door-to-door in my neighborhood the other day selling textbooks. When he came to my door he was telling me about the textbook and it's uses. He asked me how much homework I usually get so I replied "I'm actually not sure yet. I'm about to start my freshman year of college."
His exact words were "Wow....um.....sorry I thought you were in 7th or 8th grade."

Ok, I know this will be great when I'm 50 and I look younger, but I hate it now!

Is it my hair?
My hair is extremely thin and fine, so there's not much I can do with it. I usually just leave it down.

Is it my clothing?
I dress pretty casual. Usually jeans and a t-shirt, just because it's comfortable.

Is it my makeup?
I only wear eyeliner and mascara. I don't like spending an hour every day cakeing on makeup. That's just not for me.

I just don't know what to do. I'm sick of people thinking I'm so much younger than I really am. Any tips?