A lot of those who voted Yes on joining in 1975 will have been dead by a decade or two later. We didn't have a do over. I doubt you'd be saying the same if the position was reversed. I wasn't pro Leave but this kind of argument is pretty ridiculous.
Doesn't necessarily follow. If patterns of voting had not changed significantly it would have been the younger people who predominantly voted to join and the older people who voted not to, so the people who voted no would have died out.
The Brexit vote was ideally timed for peak Boomer participation and we are now a vanishing breed.
At the current time we are in a better position to understand both sides of the argument as most voters will have experience of life inside and outside the EU, and there now 'appears' to be a majority who preferred it inside.
I agree that it is probably a bit too soon to rejoin and we need to have a few more years experience of the lack of tangible benefits from Brexit and suffer a bit more being going back with our tail between our legs.
Either that or go the whole hog and ask Trump can we be the 51st state (or the 52nd or 53rd depending on Trump taking over Canada and Greenland) to save our civilisation from the barbarians in our midst.