Mine have been on adult since about 7 months. Even before then, it was the occassional adult food as well. Now, at 10months the only kitten stuff one of the two has is using up Hills kitten.

I think a good quality food is more important than whether it's kitten or adult once they have been neutered.

Wet they have mainly Tesco lamb just nature trays, sometimes turkey, and once a day share a pouch of Natures Menu adult. Kibble is Orijen and Hills kitten for one, and the other has Hills indoor (cuddly boy who gets hairballs )