There are already controls on the statistically more hazardous younger drivers. They have a lower threshold of points before losing their licence and high insurance.
Many years later, I still cringe at the memory of my first couple of attempts to pass a tractor, a skill that I didn't learn in my urban based lessons. I didn't gear down sufficiently to gain the power to pass efficiently, but it was a learning experience, and I refined my technique to do it in a much safer manner. A person in their 70-80s+ is much less likely to learn from their error. Vision, and information processing have passed their peak and can only deteriorate from that point, some sooner rather than later, some slowly and difficult to percieve, some rapidly. Some will continue to be excellent drivers into advanced old age in the same way that there are some excellent young drivers. In very general terms, younger drivers will gain experience and calm down and improve, and older drivers will find it harder to adapt to change as their mental and physical health changes.
I have a relative in her 80s at the pootling around town stage. I have no idea about the quality of her driving as I haven't observed it in years. There are certainly traffic layouts that she wouldn't pass a test on these days such as very urban areas with heavy traffic and with tram layouts/ signage that she has never encountered. Brushing up on a current highway code wouldn't solve the issue, because there is also the ability to rapidly process a lot of unfamiliar information at play. Going slow might give other drivers more advantage in avoiding or minimising the impact of an incident, but that is putting the onus on the observation skills and reactions of other drivers... rather a gamble!
If I'm driving at 60-65 mph in lane 1, I can reasonably accelerate to pass in lane 2 and anticipate that vehicles ahead such as lorries, buses or caravans might necessitate that. By the time I've registered that a Micra is going slower than expected at 45-50mph, I may not have the opportunity to have a break in traffic to safely overtake and will need to brake down to their speed. The gap in speed of lane 1 and lane 2 gets more dangerous to pull out to overtake or traffic to pull in then brake if they are approaching a junction. The driver of the slow vehicle will continue obliviously without incident, but they are creating a hazard to the other road users around them. Similar to the overly fast lane hoppers who slice around oblivious to the concept of a stopping distance leaving startled drivers in their wake.
If there were random spot check driving tests, drivers of all demographics would regularly fail, but old age (whenever it affects the individial) tends not to be an asset in adjusting habits and amending behaviour.