I have a neighbor about half my age who was been asking me about riding. I've been telling him how wonderful it is. Yesterday he went out to wal-mart and picked up a mongoose mtb. We went out and had a wonderful ride! I gave him my old Wrench Forch pump and helped him set his seat height, etc. It was the first time since I was a kid that I've ridden with someone. Well, actually we rode the other day but he was on an old junker bike he pulled out of the basement.
Anyway, we have plans to do some exploring. Most of our riding is off-road, and it involves fishing, mushroom hunting, arrowhead hunting, and that kind of stuff.
Now he's asking about racks, lights, etc.
I think I've created a monster.

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.