Complex sentence: Whilst still at Northwood College, a group of local businessmen persuaded her to start another school, and at the age of 25, in January 1899, she founded Northwood High School, later named St Helen's School.
Split into simpler sentences: Whilst still at Northwood College, a group of local businessmen persuaded her to start another school, and so she did. At the age of 25, in January 1899, she founded Northwood High School, later named St Helen's School.