Complex sentence: By suggestion of his cousin, at age 15 he started to learn boxing under guidance of V.E. Shairer (his student 2012 Olympic Bronze medalist Ivan Dychko) and Kenes Omarov with now desire to represent USSR flag on Olympic in Boxing and not in hockey.
Split into simpler sentences: By suggestion of his cousin, he started to learn boxing under guidance of V.E. Shairer (his student 2012 Olympic Bronze medalist Ivan Dychko) and Kenes Amarov. He was 15 years old and desire to represent USSR flag on Olympic games was this time in Boxing and not in hockey.