You are not alone, there are many that feel the same in regard to their own parents family being unsafe but there are mechanisms in place to support that, people just need to understand that even if you tell the DVLA that its you family member, they will not tell them that you reported them, they will call them in for an assessment.
There are things in the pipeline about the aging population and testing ability to drive but its not a full driving test. But there is also a big issue with younger drivers who know the rules of the road, but chose not to adhere to them once the tests are passed. They actually cause the significantly larger loss despite their smaller numbers in regard to the aged population. So at the moment you are focusing in the wrong place.
In the UK at the moment, younger drivers cost insurers more overall than drivers over 70, particularly those under 25. According to the Association of British Insurers (ABI), younger drivers have both a higher frequency of claims and higher average claim costs than most older age groups. [abi.org.uk], actuarialpost.co.uk]
A few interesting points:
Drivers aged 17-24 make up only about 7% of licence holders but are involved in around 24% of fatal collisions. [abi.org.uk]
ABI data shows 18-20 year olds have the highest average premiums because their claims are both frequent and expensive. [actuarialpost.co.uk]
Drivers in their late 60s are actually among the cheapest to insure, with 66-70 year olds historically having some of the lowest average premiums and relatively low claim costs. [actuarialpost.co.uk]
Once drivers reach their late 70s, 80s and beyond, claim costs begin to rise again, so insurers charge more. However, even many very elderly drivers still cost insurers less than the youngest drivers.
And the way fuel and car prices are rising, I thin the driving population my drop of its own volition.