Complex sentence: Steinberg finished a degree from Wharton at the University of Pennsylvania within two years, graduating at age 18, and has not only been a major benefactor of the school, but was also the head of the board of Wharton for over 15 years.
Split into simpler sentences: Steinberg finished a degree from Wharton at the University of Pennsylvania within two years, graduating at age 18. Steinberg has been a major benefactor of the school and was the head of the Board of Wharton for over 15 years.