Some of them didn't anyway. Robert Greene, in his pamphlet A Groatsworth of Wit, called Shakespeare an "upstart crow" because he didn't have a university education, although he conceded that he could "bombast out a blank verse with the best of you."
Nothing. Shakespeare started writing before Marlowe died.
Put where he started his writing...
We know that Shakespeare started writing plays before 1592 when he was 28. It is not clear just exactly how soon before that date he started.
When Shakespeare started writing plays, Elizabeth I was Queen of England.
It's not really known when Shakespeare started writing but it was about 1590 or so, when he was 36. He retired in 1513 when he was 49.
He started writing plays sometime in the late 1580s. We cannot be more precise than that.
Nobody knows exactly when Shakespeare started writing, but we know it must have been before 1592. Shakespeare was a kid from a middle-class country family, who had a grammar-school (high school) education.
It is not known when he started. We can guess that he started writing plays after he moved to London and became involved in the theatre scene, sometime in his lost years 1585-1592. He might possibly have started writing poetry before he left Stratford.
No one "chooses" such a profession, it chooses them. We can only speculate on what induced Shakespeare to start writing. Perhaps he started as an actor and thought that writing plays would be a lucrative and useful sideline.
We don't know when Shakespeare started writing poetry; it may have been before he was involved with the theatre. But it is unlikely that he would have started writing plays before he understood the practical requirements of theatre, which he could only have learned by being an actor.
It is not different. Literary writing is characterized by its creativity and originality.
Scholarly guesswork suggests that Shakespeare might possibly have started writing plays in about 1590, when the Queen was about 57. When she died thirteen years later he was writing more than ever, and kept on writing for ten years after her death.