This is going to be one of those times where age and skill will not overcome youth and enthusiasm. Sounds like this kid has got an excellent fitness base to start with, so the actual physical effort of riding should be no sweat. I do, however, foresee perhaps two potential problems.
The first, and most significant, will be the tenderness of his tush. Time in the saddle may not be an issue on a single day’s long ride, but remember you’re going to be doing this seven days in a row. Invest in at least two decent pairs of cycling shorts (for each of you), and have him get as much time in the saddle as possible in order to toughen up his nasty bits. Even riding back and forth to work/school/his other activities will help.
The second is the fact that unless he gets some group riding in, he will not know how to comport himself when riding in close quarters with someone else. Check and see if there is a local club or riding group in or near your home town; if there is, spend some time on their group rides. Even short rides with a group will pay significant dividends in July when you and he start rubbing elbows on the road with 10K people.