I'm from San Diego. Lotta my friends enlisted. Lotta friends I met/made after h.s. were USMC. Most, if not all (not likeninwasbtaking a survey to be cited on an internet "bodybuilding" forum 18yrs later) talked about drinking on base while underage. Drugs, weed primarily, since nobody I associated with did "street" drugs, aside from E occasionally, was frowned upon in a big way. They didn't care about booze much at that time. They'd rather have guys stay on base and party/drink if They were underage, rather than go to Tijuana and get arrested (they send MPs down to TJ jail to collect ppl Sunday/Mondays who'd gottenarrested Friday/Saturdays... Or get DUOs/arrested in the US. So long as they showed up to PT in the morning and/orndidnt miss duty, their bosses didn't care.
Dude my brother in law is a marine stationed in SD, he is a minor who drinks. If he gets caught he will be in trouble and be ticketed. College campuses are full of minors who drink. People under 21 regularly drink, it's illegal.
You said when you were being recruited you thought the drinking age was 18 on base. It wasn't. You also said that your recruiter was selling the work hard play hard lifestyle and that meant underage drinking. It was illegal.
Don't take this so personal, it's okay to be wrong.