Cool bike. I was team green in my teenage years. A KDX and KX.
The original plan was to camp at Greenhorn Mt Park.
but if the kid is coming that might change things and that's not bad. The reason being, the main access road to the better trails for him is closed for logging the burn area and the only logical way to get there while the crews are working is a diamond level trail. After 5PM we can take the intermediate trails back to camp.
I think we could accommodate him and ride slowly and help him through the tough spots but there are some areas of cliff exposure that may be unsettling on the new rev happy mx bike. Depending on your schedule, we could ride the ATV trails and such on the other side of the road for a day or two to get him used to the bike before diving in or we could just go into the Piutes instead. Piutes do not have any services, i.e., water, toilets, showers, cellular and are mostly intermediate and above trails or dirt roads. I don't mind either one as I haven't ridden in the Piutes in over a year.
Now that I've written all that, I think staying with the original camp plan and exploring the ATV trails would be the way to go. If you're ok with a 20 minute drive from camp we could drive to different trailheads and get into the Piutes or other areas for the day.