The aarp link seems to basically say that a lot of seniors are having loans rejected because of low reported income, so be sure to report retirement income.

The philadelphia fed link notes that older people who apply for loans are being denied more often, but there's lots of potential reasons for that. Aggregate economic stats, other than credit score, in the table at the end look worse to my eye near the top age brackets (but maybe not at the same levels that rejection started climbing).

It's not clear to me when it says age discrimination is prohibited, but mortality expectations are allowed. Seems like the same thing to me.

The paper suggests there may be an element of selection, which resonates with me. Looking at my parents and their siblings, most all of them would have had a mortgage 30 years ago and likely be in these statistics; now, those with higher retirment incomes also seem to be the ones that paid off their mortgages and aren't interested in a new one.