This is me
Most Helpful Guy
It's not unusual in that 18-24 age range. A lot of people don't find their first relationship until the end of that age range, sometimes longer. It's not a reflection on you necessarily. It could be your location, could be the people you hang out with, could be your interests, could even be your mannerisms or general approach. Your pictures are very attractive, but it does look like your natural at rest facial position, while not quite being 'resting bitch face' is close to 'resting disinterested face', so it could be that a lot of guys that look your way just think you are not interested and move along. An attractive woman that appears to be disinterested can be intimidating for some guys, because it appears to them to have a higher than normal chance of rejection. So a lot will skip the attempt completely.
It's hard to pinpoint exact reasons with such vague information to start with, but on a general level I think that it's probably not you, just the lack of opportunity or the lack of finding the right people with similar interests.
Most Helpful Girl
You're not alone, I'm 21 and I've never had a boyfriend either... For me, the biggest problem is that I have trust issues and I unconsciously push people away when they get too close. Maybe you have the same problem? If you make yourself unapproachable guys are gonna pick up on it and they won't approach you... Judging from your pictures, there's nothing wrong with the way you look. I think you're pretty so it's hard to see why guys wouldn't like you... That's why I think it has to do with your attitude and the way you come across. For instance, I'm quite shy and sometimes people tell me that I come across as stuck up, which is not true at all.