my boy Indy moved from Royal Canin kitten food to their Young Neutered Male just after he was neutered, as it is formulated for boys from the op (at5-6 months) on to 7 years, but kept him on kitten wet on my Vets advice.
He switched back to RC kitten when we got Misha as no matter what we do they will swap bowls at breakfast and as he is under a year still fine to have kitten food. though he does have some adult food in the evening too.
Misha was neutered early at 4 months so is still entirely on kitten food but in a month will start introducing adult dry to the mix, Although he stole Indy's last night and no bad side effects so far...

in 2 months all the dry food will be adult and will faze out the kitten wet as Misha already tends towards podgey and adult food is lower energy

according to my vet as soon as they are neutered they can start on adult food being introduced