Do cats get more rambunctious as they get older?

I actually had to Google what "rambunctious" means. Fail, me. Fail.

Anyway, I don't entirely think that's the case? My cat seems to grow more timid and... well, nonchalant as the months go by. It's not that she's sick or anything... I think it's because she's growing fat and lazy, haha, but that's just my take on it.