Complex sentence: At age 18, LeMond was selected for the 1980 U.S. Olympic cycling team, the youngest ever to make the U.S. team; however, the U.S. boycott of the 1980 Summer Olympics in Moscow prevented him from competing there.
Split into simpler sentences: At age 18, LeMond was selected for the 1980 U.S. Olympic cycling team, the youngest ever to make the U.S. team. However, the U.S. boycott of the 1980 Summer Olympics in Moscow prevented him from competing there.