There was a YouGuv poll based on a sample size of 4,772 people that illustrated this.
It was illustrated in the FT and quoted in this article blogs.spectator.co.uk/2016/06/brexit-political-awakening-young-people/.

In summary, Oxford and Cambridge people below 25 got up and voted, but most people in that age range didn't. They possibly feel disenfranchised or left behind by globalisation, but what is key is that it wasn't the old fucking it up for everyone, it was a huge chunk of Britain's younger generation saying they don't give a shit. That of course doesn't fit the narrative of bigoted UKIP tossers and is a bit harder to explain away with trite slogans.

Of course you can say polls are unrepresentative or other excuses, but the fact is that most people on b3ta got a nice education, are traveled with a open mind and are doing quite nicely thank you, so feel they have the moral high ground and can speak for an enlightened nation, but a sizeable proportion of young adults don't feel they have a future no matter who is running the country. That's a big problem and ignoring it won't make it go away.
(plankton, Mon 27 Jun 2016, 21:40, 1 reply)

My point being, 'a lot of people in this town are old, therefore all the votes here are probably from old people' is hardly scientific.

( drimble he'd been white, he'd been black, Mon 27 Jun 2016, 21:52, closed)

it's done through exit polls
which are pretty accurate
(plankton, Tue 28 Jun 2016, 11:00, closed)

Ask a certain selection of people, between 2pm and 3pm, at one polling station per town and only ask people that look like they'll tell the truth. Great.

( drimble he'd been white, he'd been black, Tue 28 Jun 2016, 19:48, closed)

exit polls are far more accurate than other polls
they got the last election right when all others got it wrong. I am sure they conduct it in a far more scientific way than you suggest, there is tremendous value in calling it right as early as possible. That's why the city conducts its own polls.
(plankton, Wed 29 Jun 2016, 8:17, closed)