Well I have a 3 year old cat named Hammie who still acts just the same he did when I brought him home at the age of 12 WEEKS!!
He still chases his tail, chases shadows, attacks everyone for no apparent reason, has BOUNDLESS, freakish energy; and is still as fearless and adventurous as I've ever seen him.
I think he's trying to show off for the older cats, really.
Snickers is 14 year old, he's aged physically (losing his sight & lost muscle mass... sort of bony in his old age
) but he is WILD at times, so wild we have to stop him. He runs around the house in this madness and with his bad eyesight & clumsiness --- he careens head-first into barstools, corners, cabinets. Last night he hit his head really hard, during his wild streak through the house!
So some cats are ALWAYS kittens!!!