Complex sentence: One team was the Juniors, who wore the blue sweaters, and all the players were under 30 years of age; the other team was the Seniors, who wore the red sweaters, and who were over the age 30.
Split into simpler sentences: One team was the Juniors, who wore the blue sweaters, and all the players were under 30 years of age. The other team was the Seniors, who wore the red sweaters, and who were over the age 30.