I don't buy this theory that is regularly trotted out by Remainers at all. It's true that statistically, the older somebody is the more likely it was that they voted to Leave. The same is true of voting Conservative and has been for as long as I can remember. So by that logic, support for the Tories should have crumbled over time as their supporters died off. So how come it hasn't?
Surprisingly it never seems to occur to supporters of the above theory that as people get older their views change - I'd call it the acquisition of wisdom. Young people are idealistic, gradually they realise that socialism doesn't work and that the EU is not the force for good they thought it was. So over time, sure some people will die but they will be replaced in the age group they have vacated by people who have become more eurosceptic, just as some will be more likely to vote Conservative than they were before.
As for in ten years time the likelihood that there will be a bunch of young europhiles coming to dominate and itching to get us back in, that's for the birds. I see zero prospect of that. Once we're out we will be out. It's just getting to the stage of being out that is the problem at the moment.