You could have chosen some one with a bit of sanity---Walmart for a bike? And you should have kept some of yours---Riding with someone half your age gets painfull.

But great to have someone to ride with. How did he get on? Did he get up the hills and slopes that you didn't is the main question. If he did- offer to service his bike for him. 15 psi in the tyres should slow him down a bit and a bit of brake binding wears people out fairly quickly.

But try to steer him off buying too many parts just yet. Get him accustomed to paying at the coffee shop first and then introduce him to the spares he should be carrying. Then you can leave yours at home to get up the hills easier.