All mine started to calm down after 1 year old. And since I like them hyper I was sad that it happened.
Confession: I'm sure a lot of it is because after they are 1 year old, I start to seriously train them. We can train up to 14 hours a week. I'm sure all their extra energy is used in when we train and that's probably why they are always so calm and sluggish when we are at home.