I'm not sure exact answers, but yes there would be a cut off. I know some females have been giving amazing clutches for 10+ years. I wouldn't think you'd have to worry about anything until they're in their elderly years (15+). But, don't quote me on that. It's just a theory.
As for personalities, to a point. I know I heard of one person attempting to breed extremely docile snakes. She took the calmest babies from a calm pairing and was going to pair them together. It may not truly do anything, but it's possible. I do know that my more excitable parents produced more excitable babies, but it may just be coincidental.