Old ale is a term commonly applied to dark, malty beers in England, usually above 5% abv, often also called Winter Warmers; also to dark ales of any strength in Australia. Sometimes associated with stock ale or, archaically, keeping ale, in which the beer is held at the brewery. American brewed old ales will tend to be of a barley wine strength.
Historically, old ales served as a complement to mild ales, and in pubs of the era typically the landlord would serve the customer a blend of the sharper stock ale with the fruitier, sweeter mild ale to the customer's taste. In London especially, the aged ale would take on a sour, lactic acid note from the continuing fermentation in the cask. Because of the time required for the aging process, some investors would buy mild ale from brewers, age it into old ale, and sell it at the higher price. Eventually, brewers began to keep some beer behind at the brewery, age it themselves and sell it to the pubs. In some cases old ale was a blend of young and old. The "stock ale" was the brewery's very aged ale and was used to inject an "old" quality, and perhaps acidity to the blend.
Winter warmer is a traditional malty-sweet English Strong Ale that is brewed in the winter months. It is usually quite dark, but not as dark as a stout, with a big malt presence. Sometimes, winter warmers have a few spices, especially in the United States, although spices are not necessarily a required ingredient in a Winter Warmer. The primary characteristic is strength; the average alcohol content by volume ranges from 6.0% to 8.0% ABV and some Winter Warmers reach 10% ABV or more.
Some brewers will make a high ABV old ale for bottling. Some of these can mature for several years after bottling, and may or may not be bottle-conditioned.
The "October" Keeping Ales are thought to have formed the basis for India Pale Ales shipped by the British East India Company.
Another version was so-called "Majority Ale," a strong ale brewed on or around the birth of a child, and intended to be drunk on the child's twenty-first birthday.