You’re way off. A generation is roughly thirty years, and industrial plastic production has been around longer than that. Bakelite was invented in 1907 and widely used in consumer goods already in the first half of the 20th century. Then, styrene was widely produced by the 1950s. You can watch Alain Resnais’s 1958 documentary film Le chant du Styrène[0] to see the vast industrial apparatus that had already been built in France to produce it.
What is true is that plastic wasn’t such an everyday feature of the developing world until the last few decades, and it was the combination of increasing plastic use and lack of organized rubbish collection that led to plastic-strewn streets and polluted waterways there.