I'm not sure why "retire" is equated with sitting on the porch doing nothing. Perhaps that is the image that some folks hold but I know lots and lots of people who fund their own existence through passive income (savings, etc) and do all sorts of interesting things. I need a different word for that state, perhaps self employed might be more accurate since at that point you are paying your own "salary".
My Grandfather retired at 45, after becoming the head-banker for a large bank in the north island of New Zealand. Got his gold Rolex and everything. He then proceeded to start, fund and get involved in a number of businesses, owns race-horses, has a massive social circle and is still going strong at 75. He's my idol, for good reason :)
It seems like leisure in the sense that Thoreau was talking about would be a good fit. Leisure"s contemporary meaning is pretty much doing nothing productive. Thoreau viewed at as doing things for their own sake, which does not preclude being productive. You can work as hard in leisure as you would for err... work to make a livelihood.
