Original: He was signed by the Bruins at age 14 and as a 16-year-old, played for the Oshawa Generals in the junior league Ontario Hockey Association, competing against eighteen-, nineteen- and twenty-year-olds; National Hockey League rules dictated that he could not join the Boston Bruins before reaching eighteen.
Simplified: As a 14-year-old, he played junior hockey against eighteen, nineteen and twenty-year-olds.