Ninety-eight percent of all port made is "wood" port, as opposed to "vintage" Port. Wood port is so called because the wine, after having been pressed off the grapes, allowed to ferment briefly, and then fortified with high alcohol grape brandy to stop any further fermentation and remain sweet, is then put into wooden barrels for aging. It is not vintage because what goes into the barrels is a mix of more than one year's (one vintage's) product. In fact what goes into the barrels is a mix not only of several years' product, but a mix of several vineyards' product. (A vintage port is usually a mix of several vineyards' wines, too, but all of a single year. Only a "Quinta" vintage port is from one vineyard and one year.)
The youngest and sweetest example of a wood port is a type called Ruby. The bottle you buy may not say "ruby port" on the label -- true port, from Portugal, must say Oporto, and quite possibly the makers of the genuine article assume they need not bother to put a generally understood descriptor (in English) beside it as well. The one ruby port that I have tasted does not explain itself as such. What is also missing from the label, and what therefore alerts you that this is ruby, is the number, 10-, 20-, 30-, or 40-, followed by "year."
When one of these numbers is present, you have a Tawny port. These will be older and drier than the (painful to admit this, but -- almost cough-syrup sweet) rubies. A 10- or 20-year old port will be a wine mixed and aged in a barrel full of doses of wines which may have been technically anywhere in the neighborhood of 9 or 12, or 19 or 21, years old at the time the whole contents of the barrel were bottled. It's important to remember, therefore, that the label announcing 20 year port is not announcing vintage port. If it were, there would be a single year -- 1931, just like the Quinta do Noval served at David Peppercorn's party -- standing proudly on the label.
There are several other types of wood port, beyond the simple ruby/tawny distinction. Actually, the remaining types are still subcategories of tawny, but they are wines which are essentially classy and flavorful enough to spend less time in a wood barrel, or wines that are not great enough to bottle-age completely, like a vintage port, but that have come from a single vintage anyway. These subcategories are Vintage Character port (a blend of wines having the character of a single great year), Late Bottled Vintage (one year's wine, aged 4 to 6 years in wood), Crusted port (several years' worth of wine, aged 4 to 6 years in wood), and Colheita port (another single vintage, but aged at least 7 years in wood). There is also White Port, made from the pale grape port varieties, and Young Tawny, made from a mixture of Ruby and White ports.
As with all wood ports, these last half dozen or so subcategories of the tawnies do not benefit from any further bottle aging after you buy them, with the exception of the Late Bottled Vintage ports, which appear to be wines just a hair's breadth away from great, capital letter, Vintage Port status.
The wood ports are ready to drink now. Ports in general were the classic finish to a fine meal, especially for men. (I wonder if its usually accompanying cigars is the reason why, to this day, a sommelier must know cigars as well as wine.) According to authors Gail MacColl and Carol McD. Wallace of the charming To Marry an English Lord, there were strict rules about port consumption, even after the ladies had left the table: port was passed around the table counterclockwise, and a gentleman who let the decanter pass him by could not change his mind and grab it back; he waited until it made the circuit of the table around to him again. The decanter was slid along the tablecloth, never lifted. This sounds bizarre and Druidical, but was no doubt practical. That vintage port in the decanter -- and the gentlemen at a fine party could no doubt afford vintage -- would have been throwing sediment as it aged in the bottle, which was why it was decanted in the first place. Sliding the decanter would ensure that any further sediment would stay at the bottom, and not pour into the gentlemen's glasses.
I started my journey into real ports with a $20 bottle of ruby, which I made sure to last probably longer than I should have. The tawnies will cost you twice that, at least. And as for vintage, well, until we all hit the jackpot, we can least look at them, virtually.