I don't believe you when you say that girls don't look at you. I can tell that you have the looks but they are hidden by your style. You can make some changes that will make you more attractive to girls. Here's what I think you should do:
1. I know you like your moustache but it really NEEDS TO GO. A 23-year-old does not need a moustache. You don't need the moustache to get into an R-rated movie or buy alcohol because you are already of legal age. The less hair on your face, the better you will look. Right now, the moustache makes you look too old, too serious. A girl likes a guy who looks mature but not someone who looks like he can be her dad. Being clean-shaven is key.
2. I also think you should get a haircut. Your hairstyle and sideburns make you look as though you are a part of the 1960s era. Step into the 21st century. Get your hair cut LOW. Not bald but LOW, like this photo below for example:
http://cm1.dotspotter.com/media/0/31/11/Paul_Walker.0.0.0x0.280x280.jpeg
Get the haircut and either trim the sideburns or get rid of them altogether. Also, as someone here has mentioned, remove any hair between your eyebrows.
3. Wear some casual clothes. Regular T-shirts, light and navy blue jeans, and some short sleeved collar shirts. You should also try buying some khaki pants. You don't have to wear the latest brand names. Just something that looks presentable. The shirt you have on in the photo where you are lecturing is the best. You should wear more clothes like that.
4. I'm having a hard time pinning down your weight/body type. I only know that you are six feet tall (which is good height). In the first photo, you look okay but in the photo where you are in the squirrel costume and in the photo where you are in that white coat, you could lose a couple of pounds. You also need some more muscle, so start hitting the gym. Work on the forearms, shoulders, abs, triceps and biceps and don't neglect the lower body (calves and hamstrings). If you are not sure what to do, casually ask some of the employees at the gym (almost all of them work out regularly) to give you some advice on how to start out weightlifting. That's what I did. Also, hit the cardio treadmills while there. Start playing more sports that allow you to break a sweat like basketball, soccer, and/or tennis. Cut down on the fast food. You will start noticing results sooner than you expect. Believe me on this one.
5. If you have the money to get braces, then by all means, go for it. If not, then don't worry about it because your teeth are okay. Just make sure that you brush twice a day. I also don't think you need a tan.
I hope that I wasn't too harsh but I think that you have what it takes to get the girls you want. Just follow my advice and you will be a magnet. But always remember, you are the prize. So be confident when you talk to girls. They get nervous just like we do. So relax, because you are not alone. And if you get rejected, move on to the next. Every guy faces rejection. Dating and women are a numbers game. The more girls you talk to, the better your chances of success will be. I hope this helps.