Let him lift now, just make sure he's using the right form but make him do heavy compound movements just like everyone else. There's no evidence backing up the fact that lifting heavy at a young age...
Don't do front squats after squats. First of all, you shouldn't be able too. Second of all, its unnecessary. Scherpenzeel doesn't know what he's talking about.
You can eat McDonalds food and gain muscle. You can eat WHATEVER you want as long as you hit your protein and calorie requirements. The traditional diet is for dropping bodyfat and you can eat...