In my opinion, id reccomend either a yz250F or crf250r, I used to have a YZ250f and I loved it, i did about 50/50 trail and track riding, and the bike held up excellent in both. even though they are designed as track bikes they were great on the trail because of the suspension travel and the fact that they were built to be flicked around and beat up. I cant say for certain with the ttr230 or crf230, but I know the yzf and crf250r have liquid cooling, and that was always nice to have. With your age/size id say youd out grow the ttr and crf230 too fast (i had a ttr125 when i was 11, and started ridin my dads kx250 at 14 and I was only about 140lbs at that point) just something to think about, also if you really want a bike thats more trails type (with a headlight and lights and stuff) the yamaha wr250f is basically the YZF with the trail lights added and a kick stand (honda has a similar one as well, the crf250x I believe)

like everyone else is sayin, make sure you dont go cheap on boots and a helmet and all. I never had a problem with fox, but ive heard alpinestar and shoei are also very good.

hope this helps!