AlmostThere! said:
It feels like girls don't take me seriously. I have this idea in my mind that girls want a "manly" man.
You can make it up in a lot of other ways. Body build, money, style, etc.
Why would I not have a problem hitting on older girls while you feel uncomfortable even though you're not younger?
In college, at the age of 19 I was driving more expensive cars than people in their 40's who've been working years and years. I set the standard as to what I'm looking for in women and that's why I was going for older ones as opposed to broke ass girls around my age who still depended on daddy and mommy's money pay tuition who just wanted me to brag to their friends as if I was just a commodity. However, the older ones saw my independence and my ability to act and be a man.
Grow facial hair is the easiest fix (I know you said you didn't like to) but if you're eager to look older, than you'll find a facial style that matches your personality. I remember when I was under 21 and wanted to go to the club on weekends, I could never get in without ID, but if I just grew my hair for a week or two and then fixed it up, I'd have a better chance of getting in.