Complex sentence: Maqdes already played on the junior tour, where he could record some success, he participated in all four junior Grand Slams where his best result was the round of 16 of junior Wimbledon he has a career high juniors ranking of 18 in the world.
Split into simpler sentences: Maqdes already played on the junior tour, where he could record some success, he participated in all four junior Grand Slams. Maqdes has a career high juniors ranking of 18 in the world.