Peter calmed down when he was about 3 years old.

But when I say calmed down, I only mean a little bit!
It helped when we got another cat for him to play with.

(have a word with Caralou)
Peter is 5 now and still behaves like he is a kitten......a clumsy one at that!
He wrecked everything.......curtains and blinds, door frames, wallpaper, carpet, the fish tank...

I had to put a child lock on the fridge to stop him getting in, but he fathomed that out after a few weeks.
As I am sure you will know though, Burmese go on a mad crazy wrecking spree, and then they come up and fuss you and are the most affectionate animals ever, and you forgive them because they are so cute!
Where did yours come from? Peter was a reject show cat.

I think the in breeding may make them a bit daft.