Goldfinger's chock full of double-entendres, suggestive dialogue, and a character named Pussy Galore. That alone is enough to give this film a PG-13 rating.
There are also many violent scenes, not that the MPAA really cares about those. Many people are shot, one guy is crushed in a car by a junkyard machine, Goldfinger is sucked out of a window, a car explodes and everyone inside burns to death, and not one but two people are electrocuted. Talk about a shock rating.