Personal opinion here

Dog food is all about profit for the maufactuer
Years ago dogs were just fed scraps these days all the dog food manufactuers want you to buy puppy food which is an arm and a leg and some have Junior food to make you buy a more expensive food than the adult food before you move on to adult food
I have fed puppy food (don't get me wrong) but I have avoided the junior food
as for age of changing from puppy to adult food - manufatuers want you to stay on the puppy food for a year or more as it is more profit for them but all mine get changed to adult food around 6 months of age.
I would do what you want to do and only YOU can make the decision when to change from puppy food to either junior or adult
good luck with your decision