Just posted the comments below to Marshall Goldsmith's Harvard Site:
I agree with Marshall, with a twist. Sure, I think it's great to do what you love until you can't do it anymore. And, I'm not sure we need to set any deadline on that. In my coaching practice I've used the hedgehog concept from Jim Collin's work (Good to Great)to help executives, especially Boomers find their next playing field.
In fact, the other day when talking to a bunch of senior police executives I asked them to draw three intersecting circles. I suggested that in the first circle they place anything that good at now and could become world class with practice and development.
In the next circle, I ask them to look at that list (good-to-great list in the first circle) and put in the second circle only the ones that they're passionate about. Note: many of us are good and could be great at things we just don't like all that much...like driving a car or conducting audits (UGH).
Then in the final circle, I asked them to look at the first two circles and figure out a financial model (a fee process/schedule) that will make them a decent salary if they were to perform the other two circles well. In other words, answer the question: How can I make a living at the other two circles?
If you spend time on this process, the chances of finding something you can love for the rest of your life are pretty good. If you can only fill in the-good-to great circle and the passionate circle (but not the money one), then you have a HOBBY...not a bad thing either.