> prices double every 7 years, which is obviously not what we observe.

It’s not? The first two things that came to mind to check are almost exactly doubled:

Case-Schiller for Seattle metro area for example is almost exactly double: https://fred.stlouisfed.org/series/SEXRNSA/

Price of eggs is almost exactly double: https://fred.stlouisfed.org/series/APU0000708111