Gen 3:17 To Adam he (God) said, "Because you listened to your wife and ate from the tree about which I commanded you, 'You must not eat of it,' "Cursed is the ground because of you; through painful toil you will eat of it all the days of your life.
18 It will produce thorns and thistles for you, and you will eat the plants of the field.
19By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return."
Adam transgressed. The folks between Adam's fall and Moses, where the law was given, were sinners, but they didn't know they were sinners because the law hadn't been posted. Yet they were dying. Why?
Rom 5:13 Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned.
Where? In Adam. Adam's sin was a corporate sin. It effected the human race, not because they transgressed, but because "in Adam" they received his fallen life indwelt with iniquity.
Therefore, when Christ as God was united to our corporate humanity, that needed redeeming, He too came under the death sentence, but not for transgression. Christ never sinned, but because He shared in the multiplication of Adam's life, through Mary, He took a condemned life. So taking our fallen humanity upon Himself didn't make Him a sinner.