How can i look my age! 18 who looks like 12 or may be 11!?

well i am almost 19 mmm but i look like a child,,, i am short! mmm i do have a childish face that is why i am scared away from make up bec i dont want to look like a 5 year old playing with her moms make up,,, i have curly brown hair which i always straighten it up but i never care to brush it,,, i dont have the body of a child but not a the body of a play boy bunny!