I actually considered something along these lines as a sideline for a while, but I think the time I'd have to invest in it would make it more of a mainline occupation.
What I'd thought on started with promoting older/classic cars as a feasible alternative to young drivers rather than taking finance on a Saxo and paying through the nose for insurance. I figured that either restoring older cars, (let's face it there's plenty of cheap old projects out there), or modifying them to be more reliable, (Zetec Cortina or EcoTec Viva anyone?), and promoting them to teenagers could be a flier.
Then I got on to thinking, well, there could be mileage in sourcing insurance for them. An older car could qualify for cheaper insurance, so it might be possible to introduce some sort of brokerage for just that. Then it started to snowball........... As they've probably never been subject to driving an old, (read RWD), car then it would be a worthwile exercise to teach them how to drive it properly and/or sympathetically. And how about teaching them how and where to source parts for their car and how to service/look after them properly?
It sounds like fun, but there's no way I could afford to invest any time in it at the moment.