If you grew up in the former East Germany in the communist era (i.e. before the Berlin Wall came down in 1989) you would never have known anything other than the communist regime and restrictions on travel until the Wall came down, but the chances are that you would have parents or grandparents who could remember the days before World War II and the post-war division of Germany. You might then have asked them why you weren't allowed to travel to anywhere in the West, and they'd have explained to you that that was because of history.
I hope that Brexit Britain is going to be appreciably different to East Germany. For a start even if the EU27 were to decide to bar entry to all UK citizens we'd still have the rest of the world to explore. East Germans had considerably fewer travel options, and economic conditions wouldn't have allowed many to travel to the more exotic parts of the communist empire.
I'm also reasonably sure there would be some East German parents and grandparents who felt life in communist times was a lot happier than what they've faced since.
Likewise, future generations who grow up in the post-Brexit UK will come to realise that they are being denied the opportunity to travel, study, work and live anywhere else in Europe that their parents' generation took for granted, and their parents will only be able to commiserate with them that that's because of history and because of the political situation.
Have any of the EU27 really said they are going to deny UK citizens the opportunity to travel to their country? That would be sad.
The opportunity to study, work and live anywhere else in the EU has always been conditional and not absolute. It would be unfortunate if parents limited themselves to commiseration rather than helping their children explore the opportunities that will still exist to study, work and live in the EU27.
I doubt the UK parents who actually took up the opportunity to study, work and live in the EU27 1992-2020 will have a significant impact in percentage terms. In 2015 the UN believed there were about 1.2 million people born in the UK living elsewhere in the EU. Not all of them will be UK citizens of course. Approx 300,000 of those were living in Spain. I don't think I'd be far out in suggesting a fair number of those are grandparents already. Another 254,000 were living in Ireland, a situation far more complex than just UK citizens making the most of the opportunities the EU enabled.
Anyway, as yet I've not seen pictures of the French, Belgian, Dutch or UK governments uncoiling barbed wire and setting up SM-70's along our facing coasts. My guess is they won't be.