Hi There,

It's wonderful to hear that your baby has been doing so well!

For the constipation I would try mixing a little bit of canned pumpkin in his canned food. The plain kind, not the one with spices. Some cats really like the added pumpkin and it is often very helpful in cats that tend to get constipated.

Cats normally lose muscle mass as they age, and they also tend to get arthritis, so the related changes that you have noticed are nothing to worry about.

Thanks so much for the update

Regards,
PHKitkat