From my experience let him have just the odd lesson until he is 15 1/2 years old. Then work towards first solo at 16.
If you are not careful he could end up doing a lot of flying before first solo which i think doesn't look good if future instructors or employers look through his logbook.
There are some that say he could crack on with nav. or I/F, but flight training does have a natural flow of building confidence to deal with the increasing work load, which jumping around the syllabus doesn't help.