At 16./At the age of 16./When the writer was 16.
題干“作者是什么時候變得對揚州感興趣的?”
根據(jù)第一段第二行At 16, I bought a book that was a collection of poems of the Tang dynasty. In it, I heard of Yangzhou for the first time. I was deeply attracted to a poem written by Li Bai...16歲時,我買了一本唐代詩集。通過它,我第一次聽說了揚州我深深地被李白的一首詩所吸引......,可知答案為:At 16./At the age of 16./When the writer was 16.