a 31 year-old is 0.8 Young...why not 0.7 or 0.9?
Well, that depends on the problem domain. If you're dealing with US Presidents, 31 would be 1.0 young. And 50 would probably be 0.9 young. If you're dealing with dogs, 31 would be 0.0 young (I'm not aware of any dogs living more than 29). Sit down with a bunch of domain experts (one at a time) and poll them. You don't sit them together because they'll probably say things like "yeah, that answer."
I've not done much research into this for quite some time (and way back then, I was interested more in GIS). And a quick survey seems to say "nope, no frameworks."