I haven't owned a car in years, but drive a motorcycle all the time in all conditions. One needs to be much more careful on a bike than in a car.

I think that there's no need for rental companies to additionally "police" their clients. If someone old enough and with a valid driver's license wants to rent something, then they should be able to do so. The other side of that is the high rate of accidents on scooters and mopeds from rentals in areas like Greece, Thailand; in the latter case the lack of medical care is big thing. The government could reclassify vehicles that are current street legal as no longer being so; but I'd be more than a bit surprised if that happened.