Interesting post.
I still consider myself a newbie to racing, even though I've been at it for a few years now. It's just that I started when I was in my thirties compared to probably most on here starting in as a kid or in their twenties. So I can still sort of relate to what you are asking and what your son is experiencing.
Getting comfortable on gate drop starts was an experience that came with some anxiety. And I knew that if I was ever to be competitive I would have to, at some point, develop that part of my race skills.
Like you said with your son, I hung at the rear off the gate, and tried to race my way up. And that was a strategy that I felt comfortable with, and my racing confidence did grow.
But what really was an indicator for me as to when I needed, and felt comfortable to change my starts, was when I knew my confidence was growing about riding in traffic. Feeling comfortable being in a pack of bikes making our way around the track.
You never quite know how your brain will react when you are in a tight group in motion like that. And again, I think that is a developed skill as well. I love the starts now, and would say they might be my favorite part of the race, because it is the one time during the race when you are going at it as a group, bumping, banging bars, roosting, and getting roosted just fighting for an edge going through the turns. If it's a big track, and you are a small class, once you separate out, sometimes you find that you are all by yourself out there, which kind of sucks.
I would also study, (and still do! ) moto video's, and intensely watch how the top racers handle themselves in heavy traffic.
As to bump to "B" or not, I think you'll both know when he's ready.
