Plastic is a pretty broad term. Rubber can be considered one and was used in the western hemisphere prior to industrialization. But the first synthetic plastic was bakelite and was invented in the early 1900s. Honestly I'm also surprised production stayed low for so long, but I guess it makes sense since it follows the oil boom.

But yeah my favorite theory this month is that plastic overproduction will make endogenous male puberty impossible, as well as natural reproduction.