My old girl... What's normal ?

Hi all, I have a girl who is somewhere between 16-18. For some years now she has very slowly lost some mass ... Nothing quick and no changes otherwise . I've taken her to the vet to be sure she is alright. Lately she has been clumsier ... I would say I noticed the last few months. I chalked it up to age but I want to make sure I'm not being dismissive. When I say clumsy, I mean she does not stand up on her hind legs as quickly and easily and sometimes loses balance. She has ALWAYS been a chin to run into walls and fall off her wheel when going to fast in the past years. I have recently named her a danger to herself in that way and put her in a smaller cage with less height but room to get around otherwise. I have never had a chin this old. What is normal and what isn't for the veterans who know ? Thanks so much guys