Complex sentence: He began drawing at an early age, attending art classes at a neighborhood boys' club when he was seven years old which he continued until he was 14, winning prizes annually in their competitions, including a John Wanamaker bronze medal.
Split into simpler sentences: He began drawing at an early age, attending art classes at a neighborhood boys' club when he was seven years old. He continued those classes until he was 14, winning prizes annually in their competitions, including a John Wanamaker bronze medal.