Old people want to leave the EU because they are simpleminded and blame their lives and problems on "migration".
Middle aged people want to leave the EU because they want higher wages.
Young people want to stay in the EU because they're generally more liberal and see "union" as some kind of vague, "good thing".
The EU was a tool for ultra capitalists. Aside from streamlining certain worker rights, and forcing some boundaries and environmental laws upon capitalists, it was/is very harmful. It didn't exist to put people first. In many cases it made wars easier.
The idea that the UK "left the EU" is also silly. The UK is a Big Fish. It was never meaningfully in the EU. 99 percent of the time, the UK got exactly what it wanted when it fought against EU laws. Unlike all other EU nations, the UK also uses its own currency, and never signed away its soul to the IMF and ECB. For example, other nations in the EU can be legally forced to bail out or lend to other nations; the UK cannot. It makes the rules, and has countless veto powers.
The idea that the UK "loses money" to the EU is also silly. Something like 0.9 percent of its GDP goes to the EU; minor. The UK is a Big Fish. Nothing significant will change by it leaving the EU.
Brexit just shifts power from one set of capitalists to another; from European businesses to the London banking sector.
The idea that Brexit will lead to higher wages and that the UK will now have "better control of migration" is also silly (Japan is a superpower with negligible immigration and its wages constantly fall as debt to gdp ratios rise). Capitalism needs a constant and fluid supply of migrant labourers. Brits might hate and scapegoat European migrants, but if they don't take them in from Europe, they're going to have to start taking them in from Africa, India and Asia. And these decisions come from the Treasury, who annually release "migration recommendations" to the other arms of the Government. And everyone listens to the Treasury, because the Treasury listens to the banks, and when it comes to banks, thine will be done.