Complex sentence: In the 1890s, the school dropped the lower grades and only offered grades 8-12 for both boarders and day students; only requirement was that all students be over 12 years old.
Split into simpler sentences: In the 1890s, the school dropped the lower grades and only offered grades 8-12 for both boarders and day students. The only requirement was that all students be over 12 years old.