I thought Jaime had lost his mind when he suggested that in AFFC. I don't think Show!Jamie is that unhinged. I always thought Jaime loved Cersei more than she loved him, and her total coldness to him for having "one hand" is ridiculous. If she had any sense she would be telling him she is so glad to have him back but their sexual relationship is no more given the war, court atmosphere and their FATHER being right under their noses. However if you human nature is any indication it's hard for people who have been sleeping together since their teen years to stop because they are "supposed to".
I noticed two references to Jaime being 40. Aging up everyone (not just the children) puts a new spin on Tywin's desire to have Cersei remarry, especially to Loras a young man with no children. Lady Olenna is correct, at 40 that's a bad prize for the heir of HighGarden. No doubt Cersei is a great beauty, wealthy and well bred but her prime baby making days are over. Not that she COULDNT have another child or two but why would you risk that for someone with no children. It would make more sense for Tywin to want to marry her to a widower for a military alliance.
Aging up Jaime means that physically he has hit his peak and now has an injury. Not that he's not a bad ass or that 40 is old (it's not, Ser Barristan is in his 60s and still kicking butt) but at 40 he needs to DO or DIE- the choices he makes now will dictate the rest of his life. I like that they brought it up.
P.S. Cersei I doubt Loras wants to be married to you either.