I am absolutely sure that old peoples xenophobia accounted for much of the result. Not all though - including me.
I am not convinced that Remain made the arguments anywhere near as clear as they are being put now.
As for Leave - it was all going to be a doddle.
I take your point regarding 18-24 stats but there was complacency across the board of Remain voters. Even Farage thought that Remain was a forgone conclusion early on the day of the vote.
I can't prove it, but reckon there would be a different result if they ran it again now.
But that's because whenever Remain did make the argument the water was muddied. Leave ran a deliberate campaign of misinformation, and pulled out whichever Brexit they wanted to counter specific points raised by Remain.
I do think there were issues with Remain's campaign, but I just don't think they were the problems you identified.
Those were, in order of importance, for me:
1. Cameron's stupid concessions: I actually think he got a pretty good deal from the EU on the concessions themselves. What was problematic about them however was A) his decision to make his support for Remain contingent upon winning them and B) raising them as an issue at all. It created an open goal for the pro-Brexit rags to say 'look, even when threatened with leaving the EU don't care about us, and they're trying to fob us off' – the actual substance of the deal was always too complicated for people to relate to beyond that emotional level – and it created Cameron as a tepid Remainer who had no real enthusiasm for the EU project.
2. Cameron's subsequent involvement in the Remain campaign. As well as a tepid remainer he was about as visually representative of 'the establishment' as you could get. It left Remain with a tough sell in many deprived areas of 'we know that it's been pretty shit for you recently, but it's not the fault of the EU and things could get worse'. That was an argument that was difficult to make when the people responsible for it being shit were in charge. Remain would have done far better running an anti-austerity, anti-Tory campaign emphasising how much money the EU has poured in to deprived areas which brings me on to three:
3. Labour's involvement with the official campaign and Corbyn's lack of involvement. What the Leave campaign realised was that they didn't have to make a coherent argument. They just had to make a lot of noise. So they had Vote Leave saying one thing, whilst talking to Leave.EU and agreeing that Leave. EU would say
something slightly different, and a Labour Leave group saying something else. Whilst you could see the advantage Remain thought they were getting from a cross-party campaign, they'd have been better off simply having several Remain campaigns stating different things. A strong, unrelated to Stronger In, Labour campaign for pro-Eu membership in traditional Labour heartlands like Sunderland pointing out that it's the Tories they should be angry with would probably have been decisive.
I don't think you can really criticise the Remain campaign itself, it was just hamstrung by the characters that were involved with is and the timing of the referendum.
https://www.statista.com/statistics/655786/export-import-vehicles-value-germany/
Export value in 2016 estimated to €220 Billion.
The EU (not just Germany) represents €38 Billion of the imported car market in the UK, about €22 Billion of that is from Germany.
http://www.acea.be/statistics/article/motor-vehicle-trade-between-the-uk-and-main-eu-partners
I got my numbers wrong but my point stands... no company or industry is going to allow a market like that to be cut off from them. Especially not in an economy predominantly corportist in nature.
Ah, good old English self-importance that got us into this mess in the first place.