Does your son have a bike with real suspension and good brakes? Is everything is good working order and is familiar with how to use it?
Mine was 8 when we started. First we shuttled South Valley Park. Then we shuttled Mt. Falcon. Then Chimney Gulch. If he can handle that, there are trails at Sol Vista and Keystone (green and blue) that he can handle.
Bike skills are only part of what is required. Teach him the rules of trail. Yielding, getting out of the way, what to do when he crashes, not stoppng in places where he's not easily seen from above are all very important to keep him safe and enjoying the experience.
The more protection he's wearing the better. Knee/shin pads, upper body armor, full face helmet, full finger gloves are all good ideas. He will go down and when he does, the more he wears the more likely he'll get up and get back on. Once he gets past South Valley Park, t-shirts and foam half helmets are not sufficient.
Forget about enjoying the trail at your speed and skill level. You're a guide whose only purpose is to protect him and keep him safe and having fun.
Most downhillers are super cool and patient when it comes to kids.
Pm me if you have q's, need more info, gear, or someone to shuttle with. I went through it all last year and the scars are still pink