KF, I believe the cutoff is 25 years. And they can't tell anybody to scrap them, you just can't get one certified if it's over 25 years old. If it isn't certified then you cannot legally put an employee in it. There is no such requirement for owner/operators.
Mine is 16 years old. I can run it for 3-4 years and still sell it for a decent price, since it will still be eligible for certification for an additional 5 years.
Oh, thanks for the compliments everybody. Mine moves pretty quick depending on where I set the auto-throttle. I can set it to 1500 rpm but it uses a bit more fuel at that setting. I currently run it about 1250-1300 rpm which will still move me around pretty quick without getting too jerky or too loud. That big old Detriot diesel droning on and on will get on your nerves after a couple hours.