My Big Guy is 21

I’m in need of some help I have my moms cockatiel and he is 21 yesterday and today I noticed he is on the bottom of the cage I took him out and checked him over he seems fine tried to put him on his perch and he sort of fell to the floor of the cage any idea is it just because he’s old to be honest I’ve never taken him to the vet always clipped his wings and everything at home my whole life
Any comments would be appreciated
Thank you