If this is a matter of speed being a real issue (say 50 in a 30 in town, etc) then my vote is with VDCdriver; restrict the driving.
There’s not only the safety issue but the potential for lawsuits, liens, bankruptcy, or even criminal charges if someone is injured or dies because of the son’s driving habits.
I went through this same wrestling match with my daughter when she first learned to drive and it was doubly tough because I knew she was speeding and my wife kept insisting she was not and that if she was speeding “it’s because the speedometer is off”. Defending the indefensible…