What year did the law prohibiting tobacco sales to minors go into effect in the US?

Answer 1

All states had laws prohibiting the sale of tobacco products to minors by 1950. These were laws enacted by the individual states, not the Federal government.

Under Federal law the FDA issued the "FDA Rule,", in 1996, which asserted its authority over tobacco products and issued a rule intending to prevent and reduce tobacco use by children. The intended regulations included prohibiting non-face-to-face sales of tobacco products, prohibiting outdoor advertising of tobacco products near schools or playgrounds, imposing more stringent advertising regulations, and prohibiting brand name sponsorship, among other things.

Answer 2

This matter is in the hands of the individual state legislatures and there is not one date on which it became effective everywhere in the US.