how to attract 16-18 yr olds

You should probably start with girls that are "legal".

I don't think it would take much to impress youngins'

I mean all you have to act is immautre I guess.

From what I remember the most important thing about highschool is having a social circle. It's all about popularity... of course when I was in highschool I didn't socialize with anyone popular... I scooted by on the fact that my body was ripped and I had that "I don't give a fuck" attitude that is so popular with the ladies... My clothing was old and tattered, and I was doing martial arts all the time, I just got a black belt... Women chased after me... Just work on developing a strong frame and women will chase after you, the end.

im in ur boat. check out my other post where i do my silk routine. thats a fun one to do and works. u can use it as an opener or an attraction routine. now i go to an all dude school down in new orleans but i no what ur talking about with the amogs. i got a few friends that are like that. the way i deal with it is to be like them but better. dont take any of there shit and become the top amog. if not try to be cool with them and u wont have to worry about fighting them for the girl. if ur gunna open a set with a guy or guys in it try doing the man to man thing. it works great.

Hey man, attracting younger chicks is the same as older ones, but a lot easier! But be careful, many young girls are so inexperienced, that theyll sometimes disqualify themselves from you. Its funny

Younger girls are similar to older ones, but there are differences. The big one to realize is that by being 18, you already have a big status advantage - unless, that is, you become that 'creepy older guy that just hangs around younger girls'. So the key is to act a little aloof and disinterested. NEVER give away the fact that you are attracted to her! Act as though she is your silly little sister, you just tolerate her because she acts cute and goofy. You are an older, more sophisticated man. DO NOT try to imitate the younger guys - act and be your age, that is what younger girls will be attracted to. High school girls think it is some impressive shit if they are 'dating a guy in college', so if you aren't in school, get in some classes somewhere and at least pretend to be working on some kind of cool career. "OMG, I met this awesome older guy who is in college studying to be a doctor" is what she wants to brag to her friends. Younger girls want to seem older and more sophisticated, and you can help them do that if you represent that frame. So go with your advantage.
Now, since you already have the built-in status of being older, don't neg younger girls - they are already insecure, and you will just make them more so, to a point that they are uncomfortable. If you are well dressed and act mature and cool, they will already think that you are probably 'too good for them' and they probably don't have a chance - don't reinforce that by negging them or talking about age like it is going to disqualify them. But also, don't say stuff like "I like to date younger girls" - just express that the age difference is not a problem by mentioning at some point that your current or last gf is 16-17 ("but she was very mature for her age - not a typical younger girl" - give her a template for what to be like in order to qualify herself to you).
Enjoy it while you can - VERY soon, you will not be able to date underage girls. Most people don't see a guy who is eighteen dating a sixteen or seventeen year old girl as a problem - fifteen, yes, so stick with sixteen or older (or go for the fifteen y/o's with MUCH caution - I can't imagine a fifteen year old being much fun to be around anyway, even if they are physically mature enough to look hot, they are still basically little girls).
Just be that cool, older college dude that she would make all her friends jealous by dating. When I was eighteen, I landed the hottest sixteen year old girl at my former school - I was friends with her older sister, and we hooked up one night when she sneaked out with her sister. I wasn't one of the most popular guys in my grade when I was in HS, but hung around with enough of them to seem like one of the popular, cool kids to the younger girls. HS girls see guys in grades above them the way women see celebrities. Any guy who is in any way part of the 'cool crowd' that HS is all about would be a GIANT bump to her status to be dating. ESPECIALLY right after he graduates. It's like they are showing that they are so mature and sophisticated that they hang around and date guys who are already at the next level.
So all you have to do is be what you are, but make sure that includes having a little bit of a superior attitude (the sure-fire way to kill her attraction is to supplicate and do things that show you WANT or desire thier attention - DO NOT try to qualify yourself to her or her friends. Be aloof. You could have any silly high school girl you coule ever want!). Just talk about how great life is being out of high school, experiencing the world (exaggerate this, act like it is so awesome to be living some kind of fantasy life where you are a rock star in some way), totally free and enjoying being an adult. If you come from that frame, you will already have so much built-in attraction that DHV'ing is hardly necessary. You can just start out in A3 - begin by getting her to qualify herself to you: talk about how some young girl was all over you at a party, and you thought she was immature. Then, when your target talks about how she's not like that, about how mature she is, agree and say something like "yeah, you seem to be pretty cool for a X-teen year old. That is cool."  Then do little things to show that you like her - get her to high-five you, and squeeze her hand. If she squeezes back, you are in there. Keep doing little kino tests like that to see if she is compliant. Turn it into a little conspiracy of two - you guys like each other, but only you two know it. Sneak off to do something alone, like smoke a cigarette - she's cool enough to go do grown-up things like that with you, but you want to get away from the 'kids' for a bit. Then you can kiss her. Then go back to the party, and act like nothing happened, like it is just normal. But every once in a while, give her a knowing look and some slight, secretive kino like putting your hand on her back where no one can see it. You will be her ultimate fantasy, and eventually she will be dragging you into a closet or somewhere to make out.
Oh, and to back up some - the place to pull this off is at parties. Find some HS parties where the more popular HS kids will be, but where it would be cool for a guy who has graduated to show up - or even better, if you can find a college-freshman kind of party and get the HS girls to go there - they go to those parties hoping to hook up with some cool, older guy.
The main things to do are to NOT try to qualify yourself - that is the biggest way to blow yourself out, to brag to her or try to impress her. Adopt the frame that you are probably too cool for HS girls - but maybe, if she plays her cards right, she is the one girl you would make an exception for. Because she is so 'mature and cool for her age'. Play into her fantasy.