Everybody does it differently when it comes to home winemaking. The commercial wineries use date of harvest. Many winemakers here prefer to use full date of bottling. It makes it easier to keep track of just how long a bottle has been cellared.
When I give away nouveau wine, I use a marker and simply write the month when it is due to mature on the label in a non-obtrusive way. Then the recipient can decide to wait or drink early. I actually hate to give it away too soon, though, because they usually drink it right up. If the wine could really grow a lot by waiting, that early taste could mean a much diminished experience.