The prophets Haggai and Zechariah were contemporaries but probably of very different ages. One commentator said that Haggai may have been one of the original captives because of the way he mentions Solomon's temple in chapter 2. That would probably make him at least 80 years old. On the other end, Zechariah was considered a young man (2:4) and was probably born in Babylon after the deportation.
God used both of these men despite the great difference in their ages. That got me to thinking. The truth is that there is no magical age that is "just right" for serving the Lord. He doesn't limit our usefulness to the ages of 30-50. In his great wisdom, he chooses to use the young and old alike — elementary through elderly. And I'm thinking that the key is not so much the age or experience but the willingness of the heart.