I didn't consider it to be anything close to a tu quoque - merely a humourous aside in a thread which lost its way almost from the start.
Driving instruction is a commercial service activity - like a shopkeeper selling groceries, like a gardener digging gardens, like a decorator painting ceilings. It is an activity governed by the law of contract. The relationship between instructor and learner is that of seller and buyer. To compare it to that of teacher and student is to misrepresent the nature of the relationship - it is essentially a contractual relationship between contracting adults. Minors can make contracts for necessities - it may be that someone 17 years of age could argue that learning to drive is a necessity, and it must often be the case that a young learner does reach the age of 18 before passing a driving test.
A driving instructor is not in loco parentis.
It could be that a young woman of 17 or 18 and a male driving instructor of 23 or 24 find each other attractive and wish to further explore this attraction. Should this be forbidden by law? What purpose would be served by this? If he were, say, a hairdresser - performing a personal service - should the same interdiction apply? What if it is the young woman who finds the instructor attractive and then makes the first move?
Should there be unwanted activity on the part of the driving instructor, the criminal law is available to deal with this. The learner could treat the contract as broken and walk away from it. I do not see any reason to codify the relationship - this would be the work of an intrusive nanny state.