As you age, you get more experience, but are less able to pound out tons of code, and spend tons of time keeping up with the latest thing.
And also why I now help teams out instead of being the 18-hour code monkey. Still love coding, but you reach the natural limits of these things and have to move on. You also reach the point where you have to start thinking long-term instead of short-term.
EDIT: I'd add that I'd much rather be the guy who knows a dozen different languages and databases, has had experience in a lot of industries, and is used to working hard and saving, yadda yadda -- I'd rather be that guy looking to get into startups than the guy who took the 4-year degree, punched the clock everyday for years, trusted his company to take care of him, and is now wondering where his future went and whom to blame.
The part about not being able to slow down or you die? I actually like that part. Technology is always changing, and I like the fact that I'm constantly challenged to find real, solid value in what I'm learning or doing. Keeps me on my toes. Although I freely admit it's not for everybody.
I coast by taking as much time as I want between gigs.
I have family members who are "normal" -- they want a 9-5 job, long-term responsibilities and friendships, and they want to forget all about work when they punch out. The don't want things to change, and they want promises they can rely on for the future. They want somebody else to worry about things changing. I respect that. I'm just not that way. I tell folks that consulting has probably ruined me for life as far as ever being a useful company man.