The DVLA have a long list of conditions that they are required to be informed about but it would plainly be a nonsense to test for them all and the large majority have little to do with age. I mainly mention eye tests because vision is known to be affected by age, creeps up slowly so can be unnoticed and is important for road safety.
As for warning time, I would have thought that once tests are designed, a year would be sufficient.
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Parents of young, organic life forms are warned that towels can be harmful if swallowed in large quantities.
