Hi Bernie!
I think the Tower of Terror would be a great race for two reasons. The first is the distance. The 10-Miler is a big challenge, but not as intimidating as the 13.1 mile half marathon. (You also have to be 14 to run a half marathon at Disney) The second reason, is that you have almost a year to train for it in a healthy and safe way.
If you aren't familiar with the
Jeff Galloway training method, I highly recommend that you research it. Galloway is Disney's official trainer and he advocates a run/walk/run method. You will set intervals for yourself to run, then walk and repeat over and over. It's a great way to get into (or back into) the sport of running. There will also be training programs that are structured for each Disney race for you to follow.
Start slowly and build your way up to a 5K. Then, once you are comfortable with that distance, find a local 10K to sign up for. Getting race day experience is extremely valuable. Plus, signing up for the races will ensure that you get your training and your miles in.
Ten miles is a long way. Just make sure that you get yourself and your son used to moving for long periods of time. Don't worry about your speed and definitely don't pressure him. I think this would be a great father/son bonding experience for you guys!
Good luck and please let me know if you have any other questions!