How safe is a new teenaged pilot?

Our 17 year old son want to fly as a passenger with his 17 year old friend who
is a brand new pilot. We think the boy is level-headed and mature. He grew up
flying with his dad who is a retired test pilot for an aircraft manufacturer.

These credentials not withstanding, I'm guessing that there is increased risk
of accidents with new pilots. We are uncomfortable about letting him fly with
his friend, but we want to be reasonable.

I would appreciate any data or guidance this group could provide.

Thanks

Peter