Complex sentence: The Hmong-American population is among the youngest of all groups in the United States, with the majority being under 30 years old, born after 1980, with most part-Hmong are under 10 years old.
Split into simpler sentences: The Hmong-American population is among the youngest of all groups in the United States, with the majority being under 30 years old, born after 1980. And most part-Hmong are under 10 years old.