I'm 31, and have just started working towards my PPL this year. It's the first point in my life where I've actually been able to afford to, and given that I a) have a reasonably well paid job (I'm a solicitor), b) am not married (the average cost of a wedding would be enough to put both people through the PPL!) and c) don't have children and have no intention to, I can imagine that many people would get a lot later in life before they would be in a position to be able to afford to learn to fly.
Having said that, my club seems to have a reasonable amount of people my sort of age around - it doesn't seem to be particularly dominated by the over-50s.