I have been lifting for many years. At my peak I did 585 on the deadlift and after only 4 weeks back dead lifting again after many years not, easily pulled 455 with very little trouble. I am very good dead lifter, but I also lost 4 YEARS because of it. At his age, I would avoid deadlifts and squats. I over developed my lower back muscles to the point I couldn't do anything. I went to chiropractor for about 2 years to get myself straightened out.
Deadlifts and squats are great exercises, but also are two of the exercises where you could sustain lifelong injury. Those movements should be left to when he is a teen, 15 or 16, where he is capable of understanding his own body. No I am not making any waves, but I think he is too young. I could be wrong, but after 25 plus years, at 7, I think you are really playing a tough game, where the risks are greater than the reward.
His form is okay, but you want to keep that bar as close as possible to your body all the way up. So your legs can help you power you through locking it out. Most people allow the weight to drift to far in front of them causing them to involve their lower back more than they should.
Good luck, but be very careful here. Make sure you are getting good guidance with him.