I would say English started out about 1300 years ago when germanic tribes stated to colonize Britain, as the Roman empire collapsed, pushing back the Celtic peoples into the north and west of Britain. The two largest Germanic groups, the Angles and Saxons formed a language called Anglo Saxon, which we might just be able to understand if spoken slowly. It is quite different to modern English. From about 940 to 1065 England was often ruled ruled by Danish Kings and much of North and eastern England colonized by Scandinavians. Norse and Danish languages became commonly spoken. After the Norman conquest in 1066, the ruling class spoke Norman French and the people spoke Old English (Anglo Saxon). The Anglo-Saxon language evolved over the next few hundred years heavily influenced by Norman French into modern English. Sorry for the history lesson, I couldn't let the above post go without a boring correction.
