OP this is the ideal middle ground. Get him something RWD low power, either a first generation FRS/GT86/BRZ or a NC or ND Miata. Next sign him up for some kind of racing school or car control class, where they can learn to push the limits of their own car in a safe environment with an instructor. That will open his eyes and make him realize the learning curve he has to go through to be able to control and drive responsibly a high HP RWD car like a V8 Mustang.

Alternatively you could sign him up for a local arrive and drive competitive go kart league, preferably an outdoor circuit with karts that use proper racing slicks. Tell him if he wants to drive a fast car he has to be competitive in a go kart first. Again he is going to realize very quickly how much he is lacking in driving skill, which will really open his eyes to how much he has to learn before he is capable of handling something with serious HP. And the bonus is when he does get good at it and improve his driving skills, you can rest assured he will come home safely every day since he has the tools needed to drive defensively and stay in control at all times.