Yup! As I was reading the article, I was pretty surprised as it continued to not mention the vastly different labeling laws in the U.S. vs the rest of the Anglophone world. In the U.K., for example, meat labeled "lamb" legally must come from a sheep that is less than a year old. Meanwhile, U.S. "lamb" is typically 12-14 months old [1], since the U.S. has no standards on sheep meat labeling, and permits all sheep meat to be labeled as lamb. Much of the sheep meat sold in the U.S. wouldn't be legally considered "lamb" in the U.K., Australia, or New Zealand.

Meanwhile India has its own, wildly different meaning for mutton: it means goat meat. If you get an Indian "mutton curry," it'll taste really different from U.S. "lamb," but that's not because of the age of the animal — it's an entirely different species!

1: https://en.wikipedia.org/wiki/Lamb_and_mutton