They aren't that old, Deny. I did have one in my truck for 7 years - then it pooched. I replaced it with another of the same, and bought a second at the same time, though I never got around to hooking it up. I doubt the one I DID use was in the truck more than a year old or so. (though that was a while ago, I could be getting a little fuzzy...)
I only swapped them out 'cuz I got a great deal on a pair of Optima Red Top blems, which are still in the 70 and working great.
If you don't care about having AGM type batteries, those Globelites kick ass, and they're cheap.
GG, you're right about Polar not pushing Optimas. The guy went out of his way to steer me away from a Yellow Top when I inquired about an in-cab deep cycle, even though the YT was more expensive. They do sell 'em though.