how did they know the age distribution in voting?

[Lucydogz]

I'm just intrigued. The only way I can think of would be from exit polls (which I don't believe were taken). Anybody else brighter than me with a suggestion?

Everyone who registers has given personal details. If they turn up to vote it's checked off a list so they know who votes and who doesn't.

Do you mean the way people voted? They don't, as far as i'm aware - it's anonymous, surely?

I've seen a chart being bandied around saying how people voted according to age, when you looked right at the bottom it was based on a pre-election poll.

Although I guess they can make assumptions based on areas - more younger people in London, and London voted remain, type thing.