Geoffrey Chaucer was born around 1343, probably in London. (Like many details of Chaucer's life, it's impossible to verify either of these facts.) His parents were John and Agnes Copton Chaucer. John Chaucer was a successful wine merchant. The Chaucers were not wealthy, but they were well-to-do. More importantly, they knew the right people. In 1357, when Geoffrey Chaucer was still in his early teens, his father got him a job as a page in the household of the Countess of Ulster. In 1359, he joined the English Army and fought in France during the Hundred Years' War (actually a 116-year war, but hey, who's counting). He was captured during the Seige of Rheims in northeastern France in 1360 and was released after the payment of sixteen pounds - a ransom paid, rumor had it, by King Edward III himself.
Chaucer would have gone to French-speaking schools and most likely spoke both English and French at home to his parents. He was born just near the end of a period of serious French influence on English life and culture. The successful invasion of England by Norman French conquerors in 1066 had left an odd linguistic divide. For the next 300 years, English was the language of the common people. The elite spoke French, including the royal court. Chaucer would not have been able to advance as a civil servant without knowing the language. And Geoffrey Chaucer was definitely upwardly mobile.