Hi, and welcome to the forum.

Having done much the same thing - only in a roundabout way - the first thing you need to do is to determine how/if you can get a "long stay visa" for France. These are not easy or quick to come by - first step might be to contact the French Consulate in San Francisco (Consulate General of France in San Francisco) and see what they can tell you about visas available for what you want to do in France.

Do see the "sticky" post at the top of the French section here. If you have the language thing covered, you'll still have to do something to support yourself, which means you will have to find a job in France before you apply for a visa. This will take quite a bit of time, depending on what line of work you are in. Unemployment in France is still quite high, particularly for young people, and coming from the US you will need some "special" skill or experience that is not commonly found in the French population.

If you are retired, you'll have to prove that you have sufficient income to support yourself in France (and Paris is an expensive city) and that you have health insurance coverage equal to the French national plan. Retirees are always at the mercy of exchange rates, and many US retirees in France are being squeezed by the weak dollar.

The other website you should study carefully is the Service-Public site SERVICE PUBLIC - Particuliers (the French pages). There is lots of excellent information available here, particularly in the Etrangers en France section. But, each prefecture and département has their own take on the rules, so just because you see it on the website doesn't mean that's how it works in your case. (One of those things you learn to deal with after a few years of living here. )

As I've said to many others, it won't be easy, but it's not impossible. Just remember things happen s-l-o-w-l-y in France.
Cheers,
Bev