Select on quality of the wine, not on some mindless vintage rating. Some older vintages are still available at reasonable prices. Lesser known vintages can be superb. Keep a few bottles standing upright so they can be poured carefully without disturbing the sediment. If you intend to sell full bottles of old vintages by all means invest in decanters and proper staff training.
Older vintages take a great deal of care to serve by the glass.
If you use a Cruvinet the wines have to be decanted and put back into the bottle. Nitrogen gas also helps. Other systems such as vacuum pumps provide limited conservation for a fine vintage port. It is quite unfair to offer a customer a tired out vintage which has been open for a week or more. Two or three days is the limit once the bottle is uncorked.