Younger Brother was ignorant of character of his Father.Sin is not a defect, sin is a given in choice. Sin is separation from God and noting more. Killing, stealing, chasing the neighbors wife is not the sin, the sin is being separated from the One who would not do those things by way of virtue. And that doesnt come by trying to follow the laws for sin, it come by a renewing of the mind to think in Gods terms for purity, holyness, perfect even as your Father in heaven is perfect and walk as He walks in His same light.
If one has the same mind, His traits become our own. 1 John 3:9 we who are born of God, born again as Jesus was in Matt 3:16, it is impossible to be in sin.
Elder Brother was not.