Why men my age won’t approach me in public?

I am a 21F i always got told how pretty I am from women, men, even kids..etc but for some reason whenever I do go out I barely get approached by men my age, it’ll happen just not as often as guys who r 30+ I also got told from my friends how i have a RBF and ppl think I’m not approachable but am I supposed to walk around smiling? Idk what exactly I’m supposed to do. I’m also a quiet person so I always stay to myself which makes It worse. Any advice?