In 2012 there were 3,768,699 drivers over 70 in the UK.
If these were to have a driving test every year there would be 10,325 driving tests every day of the year, including Christmas Day.
It is, simply, impossible.
Even if we test the over 80s, there were 1,012,399 drivers on the same date. That would be 2,774 tests every day.
In the year 2012 there were 1.43 million practical car tests so to test every over 80 driver would almost double the number of driving tests a year. To test every over 70 would more than treble the number.
Can't be done.