Alex Sarr had the most games by a player younger than 21 with 1+ steal, 5+ assists, 5+ rebounds, 30+ points and 1+ block this season, with 1 game.
Interpreted as:
most career games with 30 or more points and 5 or more rebound and 5 or more assists and 1 or more steal and 1 or more block this season by a player under the age of 21