Interesting question, as have been the answers thus far received. Starting with the last point first, I am a Pensioner (coming up to 78 in three months time). I was an International Marketing and Ad-man all my working life, and for the last ten years of my working life a Marketing Professor for two Brussels based Business Schools, teaching BBA and MBA students.
Yes, I do still work, but at my own lifelong love of graphic design, notably in the world of ‘Old Posters’ and have now published over thirty books on the subject in various sectors 'chek out on amazon.com). Doesn’t make a lot of money but keeps my brain occupied.
On you specific reasons for posing the questions, my reading here (and I have had homes here since 1992 although not always full-time residency) is coloured by my own experiences, possibly now dated of the difficulties of establishing a business in France - notaby the mass of red tape.
However I still worked out of France and ensured I did not have double taxation, which meant in a lot of cases pre-EU it was necessary to establish a business presence in many other countries Estonia and Hungary to name two. Otherwise I worked through an Australian company in which I was a partner (for publishing activities), or was temporarily ‘employed’ as a Consultant which made assorted registrations essential, and all were different country by country. NB I nver had a business in France, and never conducted any business in France as unlike all the other 12 countries I physically worked in, and the 20 others or so I did Consultancy projects for at ‘arm’s length’ all worked in English language -whereas France did not.
I believe that France is still not geared up to other languages (including English), but I stand to be corrected on this. However if it IS still the case you will definitely need at least a reasonable written and spoken French to get by - or as I have, a French wife!
As you will have seen the most opportunities here are either in the building trade - renovations of all sorts, or in service industries, notably using the Internet to service Customers around the globe if that is what you can offer - education at some level seems an option, BUT even this is a massively crowded field these days, plus there are an awful lot of Free sites to compete with as well. You would be very wise to consider what sort of ‘niche market’ you might be able to concentrate on and make a living from.
Many people will cite Gites as an opportunity, but my own investigations indicated to me that with a maximum 12-15 week season, plus a few out of season add-ons like Easter, Christmas etc., to make more than just a living you need at least three gites. However as there are many Gite owners on this site, I will always defer to their greater operating experience rather than just my more business-oriented appraisal.
Hope this adds to your fund of thoughts.