That is correct, but the application of the law by customs will be at their discretion. I've been camping numerous times between 18 and 21 years of age from Montreal to upstate NY, often we brought beer into the US by land. Sometimes we'd be asked if we had any beer/etc, we would always answer honestly. We never got any confiscated, and we were usually told "just be good and don't drive if you drink". "Yes sir!".
HTSC
Originally Posted by
Steve M
... that no importation is allowed for travelers under 21, since the drinking age in all states is 21. As to the above situation, it's the same as the Cuban cigar situation: it's called smuggling. I don't think the OP was asking about how easy it would be to smuggle undeclared goods in through Customs without getting caught, but rather was asking on what the duty-free allowance was.