In how many years did Imam Ahmad compile his Musnad?

The Musnad is one of the largest and most important collections of Sunnah. Imam Ahmad began compiling it when he was sixteen years old, and continued for sixty-two years. He intended it to be a reference for people when they differed regarding a Sunnah of the Messenger of Allah, peace and blessings be upon him. His son Abdullah later appended to it what resembled its content.