I put my son on a KX65 at age 7 (not his first bike). Depending on his height, A KTM pro jr or sr might even fit him. I don't recommend any of these as a first bike. The last time I walked into a second grade classroom, I noticed that the kids weren't all the same size. Some of them were sized more appropriately for a CFR50, while others could have ridden a KLX110. This is why knowing his size would help here. Also, you could take the kid to your local shops and have him sit on a few bikes to see what fits. If it comes down to PW80 or TTR90, the PW is cheaper but the TTR is more upgradeable (it can grow a little so he'll enjoy it longer). Another thing to consider is where he'll be riding, I would assume backyard for now, but do you think he will end up riding trails, or perhaps trying out a nearby MX track. I know it's a first bike, but he'll be pretty good in 6 months.