Final answer:
The BAC limit is effectively zero or very low for individuals under 21 as part of a zero-tolerance policy, while the legal limit for those over 21 is typically 0.08%. The National Minimum Drinking Age Act of 1984 significantly influenced these BAC limits.
Step-by-step explanation:
The BAC limit differs for individuals based on their age, with regards to the legal drinking age limit of 21. For individuals under the age of 21, the BAC limit is effectively zero or very low (such as 0.02% in some jurisdictions), reflecting a policy of zero tolerance. For those over the age of 21, the standard BAC limit for legal intoxication in most states is 0.08%.
Therefore, the correct answer to the question "How do BAC limits differ for individuals over and under the age of 21?" is that the BAC limit is higher for individuals over the age of 21. This is due to the influence of policies such as the National Minimum Drinking Age Act of 1984, which mandated a higher legal drinking age and consequently affects BAC limits. Moreover, the potential penalties and legal consequences of underage drinking and driving reflect the difference in BAC limits between the two age groups.