Oh I don't know. I was just being flippant.
Until not that long ago I was travelling round the world, single and partying. I only relatively recently settled down, with a husband who is a good few years younger, and am just trying to start my family now. I'm at a stage of life people are more commonly at in their 30s.
Most of my friends were at this stage in their 30s, except for the friends I made in 'expat' communities, who like me are settling down later. However I doubt my friends who have a more conventional timeline would consider themselves middle aged either.