Any breed can be killed at any age (I think there is a recipe of chicken pudding with a suet crust in the old 1870 version of Wrights Poultry which uses 2-3 week old cockerel culls (In those days they were prepared to work for less reward than we expect these days - plus food was more highly valued). Its just that you won't get much meat,
and personally I don't begrudge my birds a few extra weeks of running around in the fresh air doing what birds are meant to do.
What you gain from a more mature traditional bird is better flavour and less "gummy" texture
Out of interest you mention Poulet de Bresse and this
link includes the following paragraphs
The Poulet de Bresse is a' commercial product'. It is a continuous improvement of an ancient breed, the selection of breeding stock is taken very seriously. Curiously, both sexes are grown for meat production, alongside the premium capon product. The capons are produced these days with physical castration of young roosters, without anaesthetic.
The Gauloise is a very fast maturing bird. It can come into lay at 16 weeks or so, if given optimum growing conditions, and a spring hatch. The breed is capable of laying 180-220 eggs per year. To me this breed is all about meat production. At 12 weeks, it is possible for a 1500g table bird, at 16 weeks a 2.5Kg bird. If left to mature for typical pure breed ages, it is capable of 3.5Kg. This is not it's forte though, the young birds are both very tender and delicate in flavour.
Care has to be taken in choice of bloodlines if considering this breed, if a utility bird is what you wanting to grow. There appears to have been two or three imports from the Continent of this breed to Ireland in the last couple of years, and it is from Ireland that this breed is filtering into the United Kingdom.
One line, certainly appears to be possibly not a recent Bresse Selection Centre line. From a Utility point of view, this line is slower growing with the roosters not filling out at the expected age in comparison to birds of a known lineage to the Selection Centre, and the egg production is slightly lowers with slightly smaller eggs.Caponisation was carried out in this country for many years, and it results in a much faster growing and more tender bird, so apart from the growth rates not being a fair comparison, I would assume, or at least hope that caponisation of male birds is now illegal in this country -either physically without anesthetic or chemically with hormone implants.