Here's a breakdown:
* Early Childhood: Blake showed artistic talent from a young age. He began sketching and writing poetry in his childhood, likely around the age of 10-12.
* Teenage Years: By his teens, he was actively creating both poetry and illustrations. We know he began copying from the works of other poets, which honed his writing skills.
* Late Teens/Early Twenties: Blake started creating his own original works, like "The Book of Thel" (c. 1789), which are considered his earliest major works.
* Later Life: He continued writing and illustrating throughout his life, creating prolifically even in his later years.
Therefore, instead of a specific date, it's more accurate to say William Blake started writing in his early childhood and continued throughout his life.