When did Leonard Bernstein start composing?

Leonard Bernstein began composing at a very young age. While there's no definitive answer to when he started, he was writing his first compositions as early as 10 years old.

He was a child prodigy, showing a strong interest in music from a very young age. He was already composing and performing by the time he was a teenager.

It's safe to say that Leonard Bernstein's passion for composing started early and never left him.