In an April 1843 general conference speech, Joseph Smith predicted that Jesus Christ would not return before he would reach the age of 85. He said, "Were I going to prophesy, I would say the end [of the world] would not come in 1844, 5, or 6, or in forty years. There are those of the rising generation who shall not taste death till Christ comes… I prophesy in the name of the Lord God, and let it be written-the Son of Man will not come in the clouds of heaven till I am eighty-five years old" (History of the Church 5:336).
McConkie believed that "it is not unreasonable to suppose that many young men had babies at the time of this prophecy and also had other children as much as 50 or 75 years later, assuming for instance that they were married again to younger women. This very probable assumption would bring the date up to, say, the 2nd decade in the 20th century — and the children so born would be members of that same rising generation of which the Prophet spoke. Now if these children lived to the normal age of men generally they would be alive well past the year 2000 A.D." (Mormon Doctrine pp. 692-693).
Joseph Smith was born in December of 1805 and didn't come close to reaching 85. He died at the age of 38 in a gun battle while incarcerated in the jail at Carthage, Illinois.