Complex sentence: Females do not begin spawning until they are seven to ten years old, some even as late as sixteen to eighteen years old, while males begin spawning around age seven, some as late as nine or ten years of age.
Split into simpler sentences: Females do not begin spawning until they are seven to ten years old, some even as late as sixteen to eighteen years old. Males begin spawning around age seven, some as late as nine or ten years of age.