In Roper v. Simmons, The U.S. Supreme Court declared the execution of juveniles unconstitutional. They did so on 3 grounds, one of which was that the United States was the only country in the world that executed juveniles. Justice Kennedy stated:

Respondent and his amici have submitted, and petitioner does not contest, that only seven countries other than the United States have executed juvenile offenders since 1990: Iran, Pakistan, Saudi Arabia, Yemen, Nigeria, the Democratic Republic of Congo, and China. Since then each of these countries has either abolished capital punishment for juveniles or made public disavowal of the practice. .... In sum, it is fair to say that the United States now stands alone in a world that has turned its face against the juvenile death penalty.

Oddly enough, it seems that some of the listed countries are still executing juveniles. Next time a politician, judge, or lawyer argues "we are the only ones in the world to do X", a) do not believe that assertion, and b) say "so what!".