Don't worry, I am 50 years old now. This is my fouth pacemaker. I also had my AV node ablated. I am still having a wpw pattern or may be a syndrome now.
Why you didn't tell Dr McWilliams that your son's pacemaker details? One lead or 2 leads, pacing at which side of the heart (right or left), upper or lower chamber (Atrial or/and Ventricle)? Are you looking for a positive support or a real picture of his future?
One day, we had a good laughed about "normal heart". If the doctors haven't sent you to the ICU/CCU your heart is still under "normal" condition. If they want to send you to the ICU/CCU that they'll said, "your heart is NOT normal"!
I wish he will stay at "Normal" and "Good" forever.
If he has no other health issues and there are not complications with his device, there should not be a problem. There are always risks of infection of the device or leads and a risk of lead fractures, but even if these complications arise, they are usually very treatable. There is never a way to predict the future, but I would expect a normal life otherwise.
I hope this helps.