For sure - I would be interested in hearing that number as well.
Buying a house at 12% and paying it off in 17 years is impressive, but I imagine it was a little easier to accomplish in 1988.
The average home price in the US in 1988 was $104,500 and the average household gross income was $34,015.
The average home price in the US today is $433,100 and the average household gross income is $74,580 (2022).
Between 1988 and 2022, the median home sale price in the US climbed over 400%, while median household income rose a little over 200%, so during that time, home values grew about 2x faster than income. If home prices had grown at the same rate as income since 1988, the median U.S. home would cost roughly $261,650 instead of $433,100.
If someone today wanted to buy and pay off an average-priced home in 17 years on a 30-year rate, they would need to include somewhere around an additional $900 a month for 17 years. So at 7.5%, let's call it a mortgage payment of roughly $4k per month plus your taxes and insurance costs, which average around $500/month across the country ($230 insurance and $2,690/year for taxes). PLUS the additional $900 a month you're including for an early payoff. You're looking somewhere in the ballpark of $5,400 a month for 17 years. That's $64,800 a year.
With how high other expenses are, I don't see any young family being able to realistically accomplish this type of payoff without having an average household income of nearly 3x over the national average, at minimum.
So to your point, it would be interesting to learn what their family income was in 1988 and if it was over 3x the national average. I am betting it wasn't.