That is a good question; but as the life expectency of our population increases while the prospect of any of us getting social security decreases, the fact is we may be at a point where retirement doesn't happen until one is at least 70 or even older. A 45-year old entrepreneur with, let's say, 20 years experience in the field who doesn't plan on retiring until 65 or 70 still has at least 20 years to invest in the company; additionally, think of what you at 18 or 20 could have learned from an internship with someone like that. I think our culture is continually redefining what is and isn't "old"; I for one don't think 40 is truly all that old.