Hi! I have a 15 year old, and I haven't switched to a mature labelled food.
It depends on whether you like the ingredients, as well as the nutritional ratios. However, since your baby is doing so well, and as along as his wellness checkups remain good, I wouldn't change
Since my cats were kittens they were on food for either cats or kittens. Difference is kittens eat more. My cat Maggie is 6 yrs old, 9pds and eats and plays like a kitten. High motabolism
Both my boys will turn 12 years old in February, and they neither one eat food for seniors (or mature) cats. I don't recall ever feeding any of my previous cats senior food either.