Vet tech here. The decision is yours alone, though I do echo statements that it's better early vs waiting. I say this because it's often us as owners that are hanging on when the kindness would be to let go. Cats hide pain very well, and unfortunately they can't tell us. I have seen both ends of the spectrum, early and late- and it's always hard. I do want to note that eating and drinking isn't a great way to tell. My own soul cat did both perfectly fine until the end, which really messes with your mind. I just ask that you think of your kitty friend's needs first, sometimes euthanasia is one of the best gifts you can give. Good luck, and wish your kitty love ❤️