As others have said, the chances of DoE having no mental or physical impairments that would affect his ability to drive at the age of 97 are remote. However, as we all know, road conditions, weather, visibility etc impact all of us, regardless of our age and it may be simply that he was dazzled by the low sun and made an error of judgment. We don't even know that it was his mistake that caused the accident. I don't think it's a minor collision when someone ends up with a fracture. If a fracture happens in a workplace, that's designated "serious" not "minor".
Where we live there are many older / elderly drivers. DH was minding his own business walking to the bank one day (on the pavement) when an elderly lady turned the corner, mounted the kerb and knocked him down. She drove on, completely oblivious to what had happened 
. A passer-by helped DH up and both of them were just WTAF at the whole thing. It was the fact that the driver seemed to have no awareness as much as the issue of driving up the pavement that shocked them.
Another one recently drove into a parking spot at the station, hit the accelerator instead of the brake and went through the railings onto the platform. Luckily nobody was hurt but that could have been horrific.
I'm not sure what the answer is, but would be in favour of 10 yearly re-testing for everybody, regardless of age.