Final answer:
Drivers over the age of 21 are considered impaired at a BAC of 0.08%.
Step-by-step explanation:
In most countries, including the US, a blood alcohol concentration (BAC) of 0.08% is considered legally impaired for drivers over the age of 21. This means that if a driver has a BAC of 0.08% or higher, they are considered to be impaired and it is illegal for them to operate a vehicle. The BAC levels for impairment vary in different countries, so it's important to be familiar with the specific legal limits in your country.