I've never heard of mead getting too old. I have heard of a Polish mead that is aged 25 years before bottling. And I've have also been told of some meads not hitting their flavor peak for 100 years although I don't think anyone has that kind of patience.
Mead is just like wine in that is gets better with age. I made a nice blueberry mead 2 years ago. It tasted like blueberries,honey, and gasoline for the first 6 months. Then it developed more of a wine taste. Its now ambrosia.
It depends on how strong the mead is. I have a 16-17% mead (plus whatever the cherries I put in it added) that took a couple of years to mellow. I also do a pyment at about half the strength that is good to go after a couple of months.