I'm so sorry! My kitty is 17 and I'm worried about
her health failing. I would also like to throw in some support for thinking about
putting him down. It's totally your choice, and no one could ever presume to know as much as you do right now, but if he bit you he's very uncomfortable. It might be time.
As for stress, make sure you have someone to talk to. You might benefit from speaking with a therapist. Also, journaling and meditation help me.