My wife and I both had very nice jobs at Intuit for 7.5 years (she's now at a new company). That allowed us to build a nice nest egg. Instead of spending that on a down payment for a house, it's now the cushion that allows us to do it.
So, not having a mortgage to pay helps :-)
Living within your means to build up some savings also helps.
I wouldn't have been able to do this if we hadn't done those things. Which is why I'm a 31-year-old doing a startup instead of fresh out of college.