Hi Sam,
I think that at your age, weight gender combination, that the overall weight and height is going to be more of a critical factor for you, especially if you are going to be riding a lot of trails and woods with friends and family.
With Honda or Yamaha's being the preferred makes at that price point, I would look at a 2000 and up xr100, or an 2004 crf100 and up. If you can throw a leg over a TTR-125, that might be another viable option for you. The tough part is when you are looking for a used four stroke, it's easy to pay a lot for a clapped out rat that will need your attention (read moolah) fairly quickly. $1500.00 trail bike for your size, etc. I would look at a couple of these options.
The only thing that is throwing my recommendation for you is that your aggressiveness seems to be pretty high "7/10", but I think that if you do pick up one of these machines, they hold their value very well. So, when you graduate collage, and start making the big bucks, you can re-evaluate your new bike choice.
Good Luck - :cool:
Trey