original: By the age of 21, he was already recognized for composing more than 200 songs.
simplifications: By the age of 21, he was known for creating more than 200 songs. By 21, people knew he already made 200+ songs. He had written more than 200 songs by age 21. At 21 years old, he had already composed more than 200 songs. By 21, he was already known for making more than 200 songs. By the time he was 21, he was already known for composing more than 200 songs. By the age of 21, he was known for composing over 200 songs. By age 21, he was already known for making over 200 songs. By the age of 21, he was already known for writing more than 200 songs. He was already understood as having made up more than 200 songs by the age of 21.