Al the top of your head is pretty good!
I have 4 children, ages 26, 25, 22, and 19. The younger three ride. (my wife and the oldest one won't even ride on the back of a bike)
The 19 is year old daughter wanted to ride first, she had her bike learners permit before she had her car drivers license. Just barely 16 when she started to ride. Her older brothers followed suit. How do I cope with the stress? That's a really good question.
The reason I came here to the Ninjette forums was because when my daughter wanted to start riding I didn't have a bike, I found 2 non-running Ninja 250's on Craiglist one for $300 and one for $400. She worked on hers while I worked on mine and we got them both running. So one thing that helps with the stress is I know she knows how to take care of her bike.
So If your son is 17 I assume you have taught him how to drive a car already. Remember those first few times out in the car how stressful it was? Multiply that by about a factor of 10 and you get an idea how I felt on the first couple of rides with my daughter. It's calmed down a little bit, but you want stressful? Watch this video, the rider with the black helmet and camel back on the black Ninja 250 is my daughter. I'm two bikes in front of her. Video was shot by a friend. You can skip ahead to about the 4:00 minute mark for the action. Again the Sena paid for itself because I could talk to my daughter.
https://www.youtube.com/watch?v=SU0IrS7jkew
A couple of things that really helped me.
1. Here in Virginia if you are under 19 years old and even if you take the MSF class you don't get your license, you get a motorcycle riders permit. The permit comes with a couple of big restrictions. First no passengers, second you have to ride with a licensed rider over the age of 21 that is close enough to you to render assistance. Since dear old dad was the only licensed rider she knew that meant for the first 9 months she had her license the only time she could ride was if she went out with dad. That meant I controlled the ride, where we went, how fast ect...... I also took the MSF BRC so I would know what she had been taught and would be able to reinforce that.
2. I got us Sena Bluetooth headsets. As far as I am concerned they paid for themselves on the first ride. The first corner we came into she did just what she had been taught in class when you come to a turn, shift down to 1st gear. No slipper clutch on the old 250's, I heard her tire screeching and shouted "Clutch IN" over the intercom. Then we had a quick discussion as she was riding about the proper way to corner and what gear to be in. Then we practiced some corners till she got it right. Then on the second ride we were going down a little country road and she says "Dad I can't feel my shifter" I told her to take a look down and see where it was, the bolt had some loose and it was dangling. We pulled over, pulled out the tool kit and put it back together.
Another thing I have to say is I really applaud you for going with a Ninja 300 for your sons first bike. My daughter went to a high school of about 3,000 kids. She was one of two that rode motorcycles. The other one had an R6 for his first bike. He spent about 2 1/2 months of his senior year in the hospital and recuperating at home from his injuries after crashing.
It is great fun riding with your kids, it is also stressful doing so. I worry much more about them than I do about me. But I also know the joy of riding a motorcycle and I want my kids to enjoy life. Besides my daughter that doesn't ride, I still worry about her.