My $.02 -
Declaw if a cat is damaging, regardless of age. Cats instinctively 'sharpen' and 'kneed', so you're not going to stop them. My cat made my decision for me when he leisurely walked up and began sharpening his claws on the grills of my old speakers. He had already shredded up the back of our old couch, but this just wasn't going to fly. The funny thing is watching him sharpen and kneed now....we call it knubbing.
FYI...he was not a kitten at the time and he survived. It takes them a couple days to fully recover, but they're resilient and the alternatives are worse (ie giving away or putting down).
As far as the peeing goes, another thing to consider is looking at a litter out there called CatAttract. It's not going to cure any medical issues, but it will assist if the issue turns out to be behavioral. Cats sometimes start peeing elsewhere when they are stressed out by changes in their lives, etc....new baby in my case. Either way, this litter has something in it that draws them to it. It's a little more expensive, but it's worth it compared to the alternative (putting down).....behavioral problems are hard to break which makes giving them away not always a viable option. So, you have to do what you can to help fix the problem. In my case, it was a blend of the new litter, better focus on cleaning the litter box, and letting him outside to get the anxiety out of his system. Ironically, he goes outside at the same time as the two dogs.....the procession is kind of funny to watch.
