The Verdict: Clear Path
Use the spouse route instead: the spouse of a German gets a residence permit on the marriage, with no income test. Take the Germany Marriage quiz, and start learning basic German now.
Section 28 of the Residence Act gives the foreign spouse of a German citizen a residence permit when you live in Germany together. Unlike the retirement permit, it does not turn on an unpublished assessment of your finances, and it lets you work.
A spouse joining a German usually has to show basic German (A1) before the visa is issued. A1 takes a few months of part-time study, and there are exceptions where learning it is not possible or reasonable.
After three years you can normally get a settlement permit. You can naturalise after three years' residence in Germany once the marriage has lasted two, against five years for everyone else.
Plan health insurance and pension tax alongside: cover as a pensioner depends on your insurance history, and how your pension is taxed depends on the treaty with the country paying it.