Complex sentence: A review found that, at the time of diagnosis, the average age of the persons affected was 4 years, slightly over half were aged 24 months or younger, and 75% were under 6 years old.
Split into simpler sentences: A review found that, at the time of diagnosis, the average age of the persons affected was 4 years. Slightly over half were aged 24 months or younger, and 75% were under 6 years old.