Barbara,
It's a good thought to give your son the opportunity to keep up with his driving, otherwise he might get a bit rusty and practice always lead to better drivers. Have you tried
eCar Short Term Insurance? They offer
temporary insurance policies for drivers aged 25-75. You can check online whether they are going to insure your son when he turns 25 in October. If they turn him down because he hasn't held his licence for at least a year, let me know and I'll try to find an alternative option for you.