There's something corrosive to the soul about having no purpose in life. I retired once. It lasted about 6 weeks, then I decided to create the D programming language. I plan to work until my mind no longer functions. I'm not interested in retiring.
I think it's important to establish the things that give your life meaning early in life, and that they not be your job. It's sad to see people hitting 65, getting essentially kicked out of the only thing they've ever done to fill their time, then unsuccessfully try to come up with a hobby on the spot.
You can't just take up fishing when you retire. But if you take it up when you're 25, spend 40 years working so that you can have weekend fishing trips and a big 3 week expedition each year, looking forward to the day you've finally put enough into the market to ditch the day job and move closer to that one really good trout stream in Wyoming that consumed so much of your vacation time over the years, and where most of your real friends try to get out to at least once a year...
Well, that seems like a better plan.