He beat me to the post by 3 minutes and he wrote a lot more about Claire's Knee than I did.
Your last paragraph is exactly right and is what I was trying to get at in my Cassavetes comparison.
I would only quibble a bit with the following from your post: "Claire’s knee is a barrier, a test for Jerome. If he can touch the knee and go no further then he has overcome his youthful desire and is ready for his new adult life with his fiancee."
I agree that this is how Jerome views the situation. I'm not so sure (and I'm not certain that this is how you're viewing the situation) that this is how Rohmer wants us to feel about the situation. Giving in to the "quest for the knee" is exactly the sort of thing that betrays the fact that Jerome has not gotten past his "youthful desire." As evidenced by his dastardly follow through, he's still the same heartless bastard. To truly have overcome his Don Juanishness, he would have had to reject the game altogether. Instead, he is self-righteous in how he views the rightness, the properness, of his actions. He never doubts that touching that knee was a true moment of revelation for him in his progress as an adult.
Jerome only passes the "test" because he's set the limits of the test. That's easy enough for any of us. A real "pass" would have been denying himself the knee.
I'll definitely write more later if you want to keep this up.