Study after study have shown that age based testing or screening for driving ability are unfounded. Older drivers, according to these studies, do not pose any greater risk than any other age category. You can read one of these studies here, done by European Federation of Psychologist's Associations - http://www.efpa.eu/professional-development/traffic-psychology 

A Petition to the Legislative Assembly of Ontario – TESTING FOR DRIVERS 80 AND OVER

To the Legislative Assembly of Ontario:

Whereas, the Ministry of Transportation has changed the rules governing the testing of drivers upon their 80th birthday;

And Whereas, these changes include new cognitive tests that will be performed by people who are not health professionals;

And Whereas, these tests are remarkably similar to the SIMARD test the government publicly promised they would not implement;

We, the undersigned, petition the Legislative Assembly of Ontario as follows:

That the Ministry of Transportation publish the evidence they are using to support the testing requirements for drivers 80 or over; and that the government demonstrate that testing requirements are evidence-based and justifiable.