Part of the problem is that a lot of the extra wealth ends invested in the house market. This increases the cost of terrains for both old and new homes. It is also not very productive just to buy one thing to extract rents from it. ( There is value in handling the rent, building or reforming and old house).
The urban land is limited and requires government infrastructure to connect it.
Another big cost is the university.
What would be awesome is if half-assed finance bro speeches weren't being thrown around as serious macro.
I can't find numbers from earlier than 1980, but 18-44 _is_ lower, though again the rate in 1980 was just a few percentage points higher, and not nearly high enough to imply that home ownership out of high school was in reach for the majority: https://www.census.gov/housing/hvs/data/charts/fig07.pdf