Rubuta ci gaba don wannan sakin layi - Theodore ya fara aikinsa na hockey na ƙananan tare da Ƙungiyar Hockey na Ƙananan Aldergrove, a lokacin da ya kafa kansa a matsayin mafi kyawun dan wasa a cikin tarihin ƙungiyar. Nasarar da ya samu a cikin 'yan wasa ya sa ya sami zaɓi a cikin WHL Bantam Draft na 2010, ta Seattle Thunderbirds. A lokacin da yake aiki tare da kungiyar, Theodore ya zama kyaftin kuma ya fafata da Team Canada a wasannin kasa da kasa daban-daban. Ya lashe lambar zinare a 2013 IIHF World U18 Championships da kuma 2015 World Junior Ice Hockey Championships
da lambar azurfa a gasar cin kofin duniya ta IIHF ta 2019.