I've wanted a dirt bike FOREVER and now i finally have funds and time to get into it and places to ride. I'm 31, female, 5,6" 165lbs. I used to ride BMX. I'm thinking of doing mostly trail riding but some track too if I get the chance. No races or anything, just messing around. I've never ridden before but once I get the hang of things I like to go FAST and am very precise. I need a bike that can handle me: not be too slow, but be easy enough for a beginner. And it has to be light enough i'll be able to pick it up and control it. I like a challenge and like to push myself and I don't want to buy a bike I'll have to trade up in a year. So what do you think? How many cc's? 2 or 4 stroke? Any recommendations?

You fall in that tweener category, with experience, at least on BMX but smaller in stature, so I'd say a Honda CRF150r. This is a four stroke that is not as big or fast as the 250cc's but has a lot more power than the "trail bikes", TTRs, DRZs, etc.

go sit on some .. take a look at the 300- 350's .. but most bikes are tall, the weight is a non-issue, the height may be depending on what your comfortable with, hanging off the seat to stop ect .... straight up if i held the handlebars while you sat on alot of bikes, your feet would be dangling about 1 foot off the ground ..

Depending on your funds, a used KTM, BMW, Honda, Kawasaki or Suzuki would work well for you. Go and try them on for size, any of them will handle your weight and size!

I think KTM exc-450 will be good