Djinn looks pretty healthy for a 19yr old! One of our previous cats got to about 16 or 17 and was at the point where she would "jump" off a chair and her legs would just splay out and she'd land on her belly.
I like the idea of having a range of ages. we have always had 2, waited till they were no more, then bought another two. so there was always a lonely grieving process before the next set came along. There was almost a 2 years break between the loss of our last pair and the new ones.