As in settle down, buy a house, and live a more gentle lifestyle.
My cousin and her fiancee settled down at 24 and bought a lovely house and live a very grown up lifestyle, whilst my sister is the same age and is living in a flat share and still going out and having fun etc (Oh and she will earn far more than they ever will!)
Dp and I live in Central London, have good jobs but do not want to settle down, one of our good friends has just moved up north to settle down and start a family with a nice big detached house