Does it take only three beers for someone under 18 to be legally drunk in Ohio?

Most states restrict underage drinking, and anyone under 21 is held to a 0.00 limit. BTW, 3 beers within a relatively short period of time would bring most people near the .08 limit. You would need to refer to a chart or even more accurately, submit to a breath test to determine if you are close to the .08 limit.