Taxed as a retiree in Germany

German tax law is extremely complicated and for a definitive answer you should consult a professional tax consultant with experience in such international matters.
In general, your income is taxed at a sliding scale of between 0 and 44% depending on how much you earn. As an example: The average German household income of €3600/month is taxed at about 15%, leading to a post-tax income of approx. €3000/month.
Another major expense you cannot escape from when living in Germany is compulory German health insurance. Without an employer (who'd pay half the premium) you'll have to pay more than most others. If you manage to join the public health insurance scheme (which is possible only under certain circumstances and up to 55 years of age), you'd have to pay about €620/month at the abovementioned average income. If you have to join a private insurer, it will certainly cost more, but the actual amount depends on coverage and age.

That is outstanding information. I assumed since I am married to a German citizen we would be covered under healthcare that does not include a monthly premium. But we will look into that further, thank you for the response. It helps.

derps wrote:

I assumed since I am married to a German citizen we would be covered under healthcare that does not include a monthly premium.

There is no such thing!
The only way of being covered for free is as dependant (spouse or child), with no own income, of a paying member of the public scheme. Everyone else must pay according to income (in the public scheme) or insured risk (in the private scheme).

I too, as well as my girlfriend living in Germany, that a spouse is (or can be) covered
under her policy at no extra cost also.  I even saw the exact words to that extent on
the website of her insurance company.  Inasmuch as we eventually plan to marry (after I ever get divorced) we certainly hope, and need that benefit, as I am retired and will have a
limited income after the split-up.

Correct: If you have no own income (worldwide and passive income counts, too!) and your married spouse is member of the public scheme health insurance, you can be covered as dependent free of charge.
But special rules kick in after you turn 55 years of age and entry into the public scheme becomes more difficult. I don't know the exact details, so please get professional advice on this!

Beppi:
thanks for your reply, and confirmation of what I have read.
Sadly, I am sure also you are correct re my age.  Dammit!!
Do you know of any private insurance companies I can contact, or
have my girlfriend in Germany start the contact for me?  This is
beginning to overwhelm here, so I'm trying to help as much as I
can from this end.  Thank you for your time!

Tim

Private health insurers are plenty (just google “private Krankenversicherung”) and each of them has several plans plus numerous options. Basically, you need a professional adviser to figure out what you need. (Most of them live off the insurers' commissions, so no cost for you.)
At your age, they all cost more than a public insurance would (which is €170 - 750/month, depending on your income) - and based on a (necessary) health check and pre-existing conditions they might add surcharges or exclusions.