I bottled one I had in secondary for 4-1/2 years recently. All to the good (for mead - bad for beer, I've done that too, and it sucked). I'm a fan of cheap vodka in the airlock, but use what you like. 6 months minimum if you are in a great heaping hurry, IMHO. A year is good. 4.5 years was not entirely due to waiting for the mead - there was also a component of waiting for me to get back to having any time for brewing. etc - two years would probably have been plenty, and then it can age in bottles.
I do NOT taste while aging, unless I'm racking. When I rack, I'll take a sample, check the gravity, and taste-test. If I'm not racking, I leave it the heck alone so the boogey-bugs can't get in and scare it. Space and time are usually enough reason to get around to bottling - if making it dry (whether or not sparkling) you'll be moving live yeast into the bottles, so it will continue to age. Bulk-aging is more time efficient, as I understand it, so a good long time in secondary is good, but when you ned the space, bottle it and move on if it's been a year or two in bulk. Put off sampling the bottles for as long as you can manage, too.