The "little sister" type never gets the guy?

Well I'm 18 and apparently if you look at my face you would think I'm 14. (I don't like to wear make up, so I don't)

I look a lot younger also because I'm 5'1 and I pretty much have a flat chest. I'm shy,(although confident), humble, honest and really friendly with strangers who also seem shy, I try to help them out a bit. I've been told that when I talk it seems like I'm my age if not older.

I'm always overlooked when it comes to guys and everybody thinks of me as the "little sister that need protecting" type, even my new and old friends. The people I like never like me in that way, so I've never had a boyfriend.

Is it because I look so young that boys my age won't date me?
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+1 y
I don't act any younger then my friends, actually besides my looks my friends label me the mature responsible one. So basically I'm treated as the "little sister who you respect and also protect because she's so cute" Cute in the "little sister" type.
Updates
+1 y
If I wear make up and change my clothes it might seem like I'm a poser and trying to look way older then I am. My friends say I don't need it. there is plenty of color on my face as it is.(I blush easily) plus I'm not good at putting on make up.
The "little sister" type never gets the guy?
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