If you are feeding an All Life Stages food, then it’s fine for life, but I would definitely start rotating through different brands and protein sources. Feeding a single food for long periods of time can weaken a dog’s gut to the point where eating anything different at all gives them an upset stomach.
As long as you are watching your dogs weight, there is actually no negatives to feeding puppy food. It is often more calorically dense, so it is easier to overfeed, but there is nothing in puppy food that is not perfectly fine for adult dogs.