A few years ago I took my sons to Botswana for a plainsgame hunt. They where a little older than your son, but I wouldn't hesitate to take a 16 year old. Definately go 2X1 as you will enjoy watching him take his trophies even more than you will enjoy taking yours. The time together, on the truck and in the camp is priceless.
I suggest that you get him his own gun, I bought my boys 30-06s, and make sure that he practices enough to feel confident with the gun. Invest in a good camera with a telephoto lens and twice as much film as you think you need. Finally, give him a notebook and have him keep a daily journal, it will prove to be an invaluable keepsake.