“The one who sins is the one who will die. The child will not share the guilt of the parent, nor will the parent share the guilt of the child. The righteousness of the righteous will be credited to them, and the wickedness of the wicked will be charged against them.” (Ezekiel 18:20)
Apostle Paul did not know about this; hence he devised something against this in Romans 5:12-21 without thinking there exists an avalanche of proofs against this. We find variety of people acting/reacting differently in same situation: Some do more righteous acts, some do more sinful acts, and others mix them in varying degrees, one-time sinners changing into saints, one-time saints changing into sinners, some very poor people who refuse to steal, and some very wealthy people who steal in various ways… etc. This shows people choose to act the way they like which means they are not sinners from birth—resulting in all sorts of people from sinless to the sinful ones. Interestingly, even Bible makes many references to some sinless persons who lived in the ancient times (Genesis 5:24; Job 1:8; Psalm 18:23; Ezekiel 14:14; Luke 1:6 …etc.) and human capacity to perform righteousness. (Habakkuk 2:4; Hebrews 10:38)