Wow. It is very strange to suddenly find out you are 67 and we’ve been trying to answer your questions about social contributions which include health care and retirement. Such a detail should be mentioned up front. But like Beppi mentioned, your options are limited at your age with healthcare. And getting into a retirement savings plan when one is already at retirement age makes no sense! You should be more concerned with making sure your American social security benefits get paid to a German bank account once you have one, or to be deposited in an American one and transferred as needed. I think there are many countries that like to attract retirees and have things set up to accommodate them but I know next to nothing about this in Germany. Probably more Germans go elsewhere to warm countries like Spain to retire than foreigners come to Germany to do so.
And you are right that it will be good to find out about inheritance taxes at your age. If you are residing in Germany then I’m pretty certain that German inheritance taxes (Erbschaftsteuer) will apply. But I am not sure if the location of the assets also matters. Unlike in America, one is not free on the first 11 million or so. I know it is very recommendable to have a will that is clear but handwritten and signed, best notarized but this is not required.
The amounts normally taxed will depend on the type of assets and who is inheriting. For example a spouse will have a tax free amount of 500,000 Euros, a child 400,000 euros, nephews, nieces, siblings or friends just 20,000 euros. Money coming from life insurance is not included in these amounts; there is another tax free scale for that depending on relationship. Total amounts over these are taxed - but again the rates depend on the relationship. And am not sure if say any kids are not residing in Germany that if they are somehow exempt. Or possibly they might have US inheritance liability in addition. It might matter that an inheritance to a US resident comes from overseas and thus much lower levels might be tax free. Thus it might be worthwhile to clarify the US situation with a US lawyer before moving. And then if one of you dies in Germany you will likely need advice from a German lawyer as well. Whether you can find a US based lawyer familiar with German inheritance tax law is doubtful.
Such things come under the subject of estate planning and for people with millions, they should have things clarified beforehand. Most people only have a few hundred thousand worth of assets and even in Germany, once it is distributed to a spouse, kids and grandkids then there will not be much if any tax due for them.
I am including a link to the Wikipedia page about German inheritance tax – but it is only in German, no English version available.