Mozart wrote his first symphony at age 8.
Why it is true
The Austrian prodigy demonstrated extraordinary musical talent from childhood, composing complex works long before adulthood.
Source: Music History
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.