You also have the problem that the pass rate for tests has changed massively in the years since most 50 year olds took their tests in the UK. Anecdotally, it is not at all uncommon for young drivers to fail the test 3+ times (at least amoung the youngsters I know). 30 years ago it was rare to have to take the test more than 2x before passing.

That and the scandal of test slots being bought up months in advance by what are essentially touts, as well as the lack of testers you noted, make it unworkable.