Complex sentence: He was apprenticed to the lawyer George Chalmers WS when he was 17, but took more interest in chemical experiments than legal work and at the age of 18 became a physician's assistant as well as attending lectures in medicine at the University of Edinburgh.
Split into simpler sentences: He was apprenticed to the lawyer George Chalmers WS when he was 17, but took more interest in chemical experiments than legal work. At the age of 18, he became a physician's assistant, and attended lectures in medicine at the University of Edinburgh.