Replying to Looking for my first dirt bike, and wondering what to get

Hey guys, I'm looking for a first bike for me. I'm 15 years old, about 5' 8", and I weigh about 135 lbs. I have been riding my friends Kawasaki klx140 for a while, and have ridden his '07 Kawasaki kx250f several times. I want to get a bike of my own, preferably a 250 4 stroke. I was just wondering what suggestions/advice you guys could give me in finding a bike, as far as what bike would be the best, etc. Most of what I will be doing with it is riding at gravel pits, and up canyons, mostly on trails though. I definitely want a bike with a manual clutch too. Thank you all for your help! It is much appreciated! I will be buying a used bike for sure though, in case you were wondering. Again, thanks.