How long is the lay over for the plane change? I might be a little biased due to our experiences but my son could have done it no problem, may not be comfortable, but he could have done it. Hell we went to Jamaica 4 years ago and he was more observant and re directed us when we were about to head in the wrong direction. If the lay over was 2hrs it shouldn't be bad, 45 minutes can be tight for some experienced flyers,
Airlines have apps that update you and also have maps of airports to see where the gate are and what the flight schedule is. Again it all comes down to your sons ability and I would be the same way make it easy as possible, but even as an adult things change and go wrong when flying so I understand your concern, things are definitely different now.
I flew out to Wyoming with my cousin at 12 years old in the 80's, we got bumped to a puddle jumper for our return flight. Prop job over the Rockies was interesting at that age. Then from Denver we flew direct to Toledo, stewardess asked us what mistake was taking us to Toledo. LOL I said it's our home. She didn't ask any more questions after that.
My sister booked me a flight 8 years ago, I had to take her back to NC after she donated a kidney in Cincinnati, I was to driver her and her car back. Lay over was 30 minutes in Dulles, biggest mistake ever. Our plane waited for another to leave the gate before we could deplane. Then I had to ride the "shuttle" which is a big scissor lift with a canvas top on it, to another terminal to catch my next flight. Never had a chance to make the connecting flight. Ended up calling a friend in Louisville KY, he was able to pick me up in Covington just over the river and take me to my sister. I will never let her book flights for me. and never go to Dulles unless it is my destination.
Your assessment of his capabilities and comfort level will all be your determination, but I wouldn't put much faith in the airlines now days. Give him the tools to and prep him anyway you can. Hopefully it is a great experience for him.