A vintage wine is a wine composed of grapes harvested within a specific year. If there is a date on the wine bottle then it is considered a vintage. These wines are usually bottled together as a single batch which ensures that each bottle produced by that vineyard is similar in flavor and quality.
Weather has a strong role in the characteristics of the harvested grapes thus affecting the flavor of the wines. So each vintage, even from the same vineyard will have its own distinct flavors and characteristics. A fantastic growing season makes for a better vintage, a poor growing season produces grapes with a lower sugar content and which leads to a lower quality wine.
Age does not necessarily play a factor in vintages, it simply informs you of the year the grapes were harvested. An older vintage does not always mean a better wine. If the younger grapes were from an exceptional growing season then that wine will almost always be better than a vintage created from grapes during a poor growing season. Many vintages do improve with age. A poor wine, when aged well and stored properly, may improve in quality and manage to rival a younger vintage from an exceptional growing season.
Many times the vintage year is unimportant as many wines produced today are meant to be drunk young and fresh. These wines will not improve with age and their quality may deteriorate. In these cases the vintage is only important to let you know if the wine would be beyond its prime.
Overall what matters most is your personal preference and your intentions for the wine. If the wine is to be stored in a collection for a while then it is suggested that research is done to ensure that the chosen bottle will age well. However; if the bottle is to be consumed within a matter of months the vineyard itself may play a larger role in your beverage choice.
Vintage itself is not a large matter for something you plan to consume. If you find a wine that you are particularly fond of then continue to purchase it. Personal taste is all that matters. Vintage wine is quite often nothing more than a catch phrase tossed around to make people sound knowledgeable. Now you can be the one that sounds knowledgeable.