My son is now 18 and we hunt together all the time, though our time together has is not as much as it used to be now that he's off at college. The first out of town big game hunt I took him on was a bear and caribou hunt in Alaska when he was 12. He shot one of each on that trip.
Since then he has been on other trips with me, though mostly we hunt around Georgia, primarily at my farm.
As for Africa, I started dreaming of taking him there before he was born. Because of the great experience of a family friend, I decided I wanted to take my son there between high school and college. After researching the idea significantly for several months, I decided to take him with me to Tanzania, but the logistics of the trip (his projected college schedule, the availability of the hunt I wanted, ect) delayed the trip until the summer after his freshman year in college, which will be July of 2005. We'll be hunting lion, leopard, buffalo, ect on our hunt. And as things have worked out, I think I'm going to like the timing of this trip better than what I originally had in mind. Since he will have been off at school for a year by the time we take this trip, I think our time together will be even more appreciated.
One thing that I decided on that you may also consider are the 2x1 configuration issues. Since basically all of the trophies will be coming back to my house, I knew that I didn't need two bags of animals coming back to my home from a 21-day Tanzanian safari. Another issue was whether or not the two of us, hunting together at all times, would have the time to actually hunt for two full bags. I discussed this with the two safari companies that I was considering. They were Luke Samaras Safaris and Legendary Adventures (Tanzania Gametracker Safaris.) Luke said that I would have to buy the two full bag hunts. TGTS said that I could take my son as a "companion", pay less per day for having him along, and that we could each hunt and split the one bag. For us, the flexibility offered by TGTS made the deal and helped me finalize the trip.
I think you should do it!