I am trying to find a good off road bike for my 13yo son. He is almost 6' tall and 165lb. He has ridden 4wheelers off and on since he was about 8 but they were all old and worn out so after a wk or two they stop running and too expensive to keep putting money into. I am hoping to get him something new this year and have been looking at the Baja DR70 700cc Dirt Runner at Tractor Supply, Minibike Warrior WR65 196cc or the Baja Warrior 90cc Dirt Bike at Norther Tool and Equipment. I can only spend about $500-700. I just don't know what is age and size appropriate and what will be durable and fun for him. We live on a 100acre farm so I want something that can take some abuse with the terrain. Any answers or suggestion would be appreciated.