The Verdict: Not eligible
You do not need a retirement permit: as an EU, EEA or Swiss national you can move to Germany and retire there freely. Register your address at the local Bürgeramt within two weeks of moving in.
Free movement for people who are not working assumes, in principle, that you have enough resources and full health cover. It is a background rule, not an application you have to pass.
Sort out health insurance before you move. Whether you can join the German statutory system depends on your insurance history. If you draw a pension from another EU state, an S1 form may give you statutory cover in Germany at that state's expense, and it is much harder to arrange afterwards.
Check how your pension will be taxed. Germany taxes residents on worldwide income, and which country may tax a pension depends on the tax treaty and the type of pension.
If you later want German citizenship, it takes five years of lawful residence, German at B1 and the naturalisation test. Free movement counts as lawful residence.