I have several storage arrays where a significant number of the drives have been powered on between 25,000 - 30,000 hours (2.8 - 3.4 years). These drives have no other issues or errors.
What I want to know: is there a point where drive age alone is a significant enough factor to replace a drive, even if the drive is working fine and has no errors?
(I'm curious to see if people tend to run drives until they fail or start throwing errors, or if anyone takes a proactive approach at replacement using Power On Hours as a metric.)
Drive manufactures generally quote MTBF on enterprise drives at 1,000,000 to 1,500,000 hours, but these numbers don't really mean much in the real world.
I did locate this study completed in 2007:
Disk failures in the real world: What does an MTTF of 1,000,000 hours mean to you?
The study suggests a "sweet spot" between 1 year and 5-7 years where you can expect less failures. Drive age before/after these times tended to be considerably higher.