How long has sin reigned? ..... 1 John 3:8 .....'He that committeth sin is of the Devil; for the Devil sinneth from the beginning.' ..... So we have had sin from the beginning of this world, but the important question is, can sin exist without there being any law? .....
Romans 4:15 .....'Because the law worketh wrath; for where no law is, there is no transgression.' ..... So if no law existed, then there could be no sin and no one could be found guilty of sin because there would be no law to sin against. So if we have had sin from the beginning, then it stands to reason that we have had the law of God from the beginning (way before any Jews were on the scene).