Complex sentence: By the age of 14 Ak had already competed in numerous amateur tournaments, but while his younger brother would move on to sign a professional contract with boxing promoter Don King, Ak realized that he wanted to pursue other interests and walked away from competing.
Split into simpler sentences: By the age of 14, Ak had already competed in numerous amateur tournaments. While his younger brother would go on to sign a professional contract with boxing promoter Don King, Ak realized that he wanted to pursue other interests, and walked away from competing.