He could kill himself or someone else. As a parent, I would not let my 16 year old drive without me in the car if they were running stop signs at all.
I do have a 16 year old son. He just got his license. I'm very grateful he has little desire for such freedoms. He's pretty good, for a new driver, but he just doesn't have a need to drive himself around and he still drives nervous.
Best of luck to you. The pain of doing the right thing now will avoid bigger pain down the road.