Which KTM mini would be a good bike for a 7 yr old just coming off of a PW50? I was looking for a used one, but have heard that they are not very durable. He is wanting to race MX, and I just want one that will let him learn how to ride without scaring him. I am considering just letting him learn on a KX 60, but I think it might be too big of a jump right now.