Even infants, who have no personal sin of their own, suffer pain and death. Now the Scriptures uniformly represent suffering and death as the wages of sin. It would be unjust for God to execute the penalty on those who are not guilty. Since the penalty falls on infants, they must be guilty; and since they have not personally committed sin, they must be guilty of Adam's sin.
("Reformed Doctrine of Predistination" by Lorraine Boettner)
I've never seen "imputed sin" in Scripture, but I'm starting to see how they get there.
The "wages of sin is death" - did that mean spiritual death, or temporal death? (Note: there is a whole different topic of whether or not physical death was on earth before the fall)
anyway, if human beings did not die on earth before the fall, and the wages of sin is (including) temporal death, we are suffering the wages of Adam's sin.
If a Just God would not punish a person (save Jesus, who voluntarily stood in our place) for the sin of another, does this logic place the guilt of Adam's sin on us, since we are paying the penalty?