I'd have flexible plans so you don't have to push him if the longer distances don't work out, and just to allow for more spontanaity.

Of course the last trip with my 13-year-old grandson, he was running me into the ground! Fortunately, the purpose of the trip was fishing. We hit the first lake a mile from the trailhead. He wanted to fish a while. After about 40 minutes he caught a 10-inch cutthroat, so I didn't even ask--I just found a good campsite and unpacked!

There does come a time, and I'm there with this grandson, that you load the kid up with all his own gear, including food, and half the shared gear, and hope that will help you keep up with him. It may be that next summer he'll carry my food, too!