I knew an ex Spitfire pilot who was in his 80s and used to turn up at the flying club to take a Cessna 150 with an instructor for an hour every few weeks. He no longer held a medical or licence.
This is slightly different as students are investing a lot of money on track to the Goal of being a PPL which means you are competent and safe to carry family and friends solo.
Some never achieve that ability but those types should be weeded out early on or whatever the problem sorted and I find it strange that this instructor tells him to consider chucking it in after he has probably spent £15000 on flight time.
Maybe a good chat and a plan with the CFI might sort things or go to another school for an appraisal flight with a new instructor and an experienced one
Pace