When did Joseph Conrad learn English?

Joseph Conrad learned English as an adult. He was born Józef Teodor Konrad Korzeniowski in the Russian-held part of Poland in 1857. His first language was Polish and he did not learn English until he was approximately 20 years old when he first entered the British merchant navy. By the time he began writing, his command of the English language was so excellent that his readers and critics would never have guessed he was not a native speaker.