Read up this thread, lots of good info and will save you asking a lot of questions that have already been answered.
https://cervens.net/forum/index.php?threads/33-years-old-preparing-for-joining.22003/
This is a bit from one of the posts, pretty much answers
"If you want the things to go quickly, come on Monday or Tuesday at Aubagne, you will be
bleu in the same week, and next Thursday will go
rouge or go home. I came on a Monday, Tuesday I had medical, sports and IQ tests, Wednesday I was selected for blue, and the next week I did not pass the commission for
rouge. I spent exactly 10 days in Aubagne;"