Although this statistic includes Gen X, I'd say the 2 million over 50s private renting definitely wouldn't agree they were responsible for the housing problems.
They're victims of it. Arguably more than younger people. Because not only are they often ignored in housing discussions, but also given their age (and the fact that data indicates older renters are the poorest group of renters) they have much less chance than younger people of ever being able to buy.
There's also 4.6 million over 50s still to pay off their mortgage.
Also RTB still happens. So while some young people are doing RTB, other young people are struggling to afford decent housing. Just as with the older generations inequality within the same generation continues to be a thing.
But agree that downsizing isn't the answer in many cases. Moving home is always psychologically hard, and as people get older it's also physically hard.
Also, as well as the shortage in many areas of suitable homes, downsizing unfairly harms single people, childless and childfree couples, and only child families. They deserve decent affordable homes too.
Agree the housing problems are the fault of government policies, not individuals of any particular age group. Both Tory and Labour governments.
And the answer is more social housing, for all who need it, young and old families and the children/childless.