Suzuka Ryūgo

Suzuka Ryogo (鈴鹿 竜吾) was only a high school student when he competed in SASUKE 4. He wore #54 and was completely cut. The only way he was known to have competed was at the end of the First Stage where his name was one of the 37 people to have cleared. He was sixteen at the time, making him the youngest person to clear the First Stage. According to the Japanese wiki article, he is still the youngest to clear.