The words of the original commandment are translated from their original Jewish context into a form which applies universally to Jew and Gentile. The commandment given to Moses was, ‘that your days may be long, and that it may go well with you in the land that the LORD your God is giving you’ (Deuteronomy 5:16), but Paul now re-expresses this as, ‘that it may be well with you and you may live long on the earth’.
God observes the ways and the thoughts of each one and even in this life gives them a partial due reward. The great application is in church life. If you make 19-year-olds the elders (yes, there are exceptions), you will destabilise the church. That is why you do not use youngsters to lead worship; it encourages them to be precocious.