The first set of numbers are of first-time buyers who managed to buy. That doesn't really speak to housing being affordable, it speaks to what circumstances people must be in before they feel comfortable buying. Median personal income is about half that [1].

[1]: https://fred.stlouisfed.org/series/MEPAINUSA672N

I don’t think the median individual income is the right reference point for mortgage affordability. Do we think that single people who just graduated high school should be able to buy a house in order for housing to be considered “affordable?” If not, it might be appropriate to compare median housing prices to median incomes of groups we expect to be able to buy houses. Median income for family households was $77,000 in 2016: https://www.census.gov/library/publications/2018/demo/p60-26.... Median income for married couples with both spouses working is $111,000: http://www.aei.org/wp-content/uploads/2018/09/census3.png.

Single people that just graduated high school used to be able to afford to buy a house. In some parts of the US they still can.

Part of the change is we stopped building cheap houses. Building a good 600sf house for 20-25k is very possible. Land costs are also an issue in some areas, but much like the car market people build based on who’s buying not the low end of the market. The profit margin is vastly better if you aim upscale.

They did? When did that happen? My parents --- upper-middle class, college-educated --- started their family in a series of small apartments, and certainly never owned houses when they were single.

Most famously post WWII GI bill provided mortgages to a lot of people without a collage degree. It helped them get a mortgage but they still has to pay the bills. It even still only ~5% of the population had a collage degree yet home ownership was common.

Prior to this people would often live with their parents or other other family members, before buying or building a home. Though this was far less common around cities.