It doesn't make sense to give someone a chance when if you are much faster than them. Should Lewis leave now to give Ocon or another Merc driver a chance? He's not much younger than Fernando. What is the cut off? Perhaps F1 should have an age limit, or a career time limit. e.g. 15 years in the sport.
5 years younger is a fair amount when it comes to sport. He's also only been in the sport 13 years, so he's got a couple more to go by your proposal.
It's only in very modern times that the drivers have been so young. Mansell won a GP at 41. Hill didn't even start in until 31. It's not like F1 is that physically demanding compared to athletic sports like boxing, MMA etc.. two areas were you get champions well into their 30s and early 40s.
So all the drivers being in shape is just a coincidence? It's incredibly demanding.
EDIT: Another point on this. I would like to see a minimum age limit with the possibility of an exemption if mad-crazy talented. That would stop RedBull destroying all these young drivers.
How do you define "mad-crazy talented"? Compared to us mere mortals, even F3 drivers are extremely talented, where's the line?