Arnold - Every system of merit, as regards licencing, where necessary skills are declining with age, is based on testing and assessment, not a set age.
I know people in their late 50's who are already doddery in their thinking and responses - and I know people of over 80 who are sharp as tacks.
If intensive control skills are required to be at a minimum set level - for everyones safety - then assessment of the individuals abilities and responses is the only way to go.
The basic problem is trying to get people to understand that their skills have declined below a safe level, when such has been determined by testing and assessment.
Accident stats, in every industry, reveal that many highly experienced older people, commit grave errors in operation of equipment and machines that results in fatalities and serious injuries.
Those errors are in direct contravention of the common belief that "there's nothing that beats experience".
Unfortunately, long experience quite often leads to complacency, the slow ingress of bad habits, and inadvisable risk-taking.
Add in the very slow neuropathic decline in brain function that affects us all eventually - and the risk of accidents, fatalities and injuries slowly increases with advancing age.
These factors are something we all have to actively be aware of, as we age, and guard against their creeping in.
Many older people are aware of their declining abilities, and actively limit their operations to ones they know they are sure of, and within their capabilities.
Unfortunately, not one us likes to be told by a younger person, that our skills are not up to scratch, and our licencing will have to be downwards-adjusted accordingly.
But it's a fact of life, that if we ignore a reasonable assessment that our skills have declined below an acceptable level, then we are only one step away from an accident.
There's some extensive and interesting medical discussion in the link below, dealing with increasing cognitive impairment - not just 100% age-related, but with many other additional factors, discussed as well.
Poor or disrupted sleep patterns are one of the additional factors that reduces cognitive impairment. With more than one additional factor adding to the age factor, the potential for cognitive decline is quite alarming with increasing age.
Age-Related Cognitive Decline