I would get him a knife for certain; any knife will let him know that you're interested/participating in something your son is passionate about. I wish my father had been so accomodating when I first got into knives.
However, making knives on your own is not, by any stretch of the imagination, an easy task. You need to be proficient at forging, heat treating, milling, machining, filing, grinding, and sharpening the various steels involved, not to mention carving the handle material.
So if you could tell me offhand what the ideal austenizing temperature of S30V steel is, or what the best methods are for carving and polishing stag horn, then by all means proceed. Otherwise, my advice would be to get him a knife made by someone else.
In either case, your idea about making handles from the antlers of that deer is (I think) a wonderful one. You won't just be making a functional knife to give to your son, but you'll be creating a family heirloom with an intimate history; you might even have a story to tell your grandkids. What an honour that would be, eh?
Still my earlier advice stands: if you aren't a skilled knifemaker, I would have the work itself done by someone else. The most important part here is making sure that the knife you give your son is a good one; whether you yourself make it or not, this is the most important part of letting your son know that you're trying to play a role in his interest. If you haven't the skill to do it yourself, then surely he'll understand, but it's the quality of the gift you give him that best demonstrates the thought involved. You can always have someone else carve the antlers; maybe someone professional, who can do a better bang-up job than either one of us. Then the thing you end up giving to your son will be something you can keep in your family forever.
