I think they mature over time, it's not a sudden thing but in my experience it's around the 2 year old mark.

Milo has always followed commands very well, he picked everything up very quickly too.

We got him when he was 7 months and thought we would have a big job on training him as he knew nothing, he wasn't even fully toilet trained.

But he would do anything for Burger King fries so that's what we trained him with, he literally learnt commands like sit, lay, stay and come after being told 3 times.

He was very, very boistorous up until the last 6-7 months (after his second birthday) where he has noticably calmed down. He still goes wild running through the woods and playing in the garden but he is much calmer in the house and more independant too.