The SmallestCub said to me, as I limped (this week's ailment, dodgy ankle) into the lift after collecting him from Art Club, "Mummy, I think I know why bits of you are so creaky. Is it because you're very old?".
Harrumph.
We actually had a long tandem-shouty-loud conversation all the way home about the whole growing up thing and concluded that 'middle aged' is the vague amorphous bit between being a Young Person (with it's very many subcategories) and being Old. And that I'm actually middle-aged. Possibly with Old ankles/knees.