Well, it really depends on the cat. I would give a percentage of about 90% do indeed settle down quite a bit even after their first birthday, much more by their second, and even more from then on. There are some, though, that stay quite goofy, such as our little Sunny. Our babies had their first birthday in April, and I've noticed that our male, Hobbes, has settled down quite a bit, but she's as crazy as ever (I suspect because she's rather small).
We had a cat when I was little that was about 5yrs, and was INSANE...would climb the drapes and race around the house on a regular basis...so much so that Princess is talked about to this day!
If you don't want them to settle down too
much, you could keep playtime going by getting them all excited with their favorite toys and playing with them regularly as they get older...but once past their first birthday, the kitten crazies don't really ever return full-blast, unfortunately. That is, except for those few that insist on being an eternal kitten...lol!!