Cane corso x presa puupy?

i need someone with experience of the breed.... if u dnt have experience do yourself a favour and comment somewere else.. i have a 5 month and 1 week old puppy, and i know you are supposed to change from puppy food to adult food earlier to stop growth problems but i dont know when to do this.. he is about 22kg and about 17 inches tall at the shoulders so im not sure...i give him purina bakers complete puppy and pro plan puppy food (since last week i only give him dry food as he got a lil diaroah from wet) my vet has no idea as he said he has never heard of the breed!!!! and theres no other vets around where i live