Po bidau gustang the leader of bidau family is being called as young man here and he calls the person on the radio as old gentle man.
from the conversation between gustang and the other person, the least that can be said about the other person is way too older than gustang to the point where he can call one of the 10 warriors a young man. he also holds equal or more authority than gustang otherwise he would've called him young master instead of young man even if he was one rank below him.
the only person that fits the description who is way older than gustang and is on equal or higher position than him in the tower is Molic One P. GR.
Molic one P.GR is one of the three lords who rule the tower and might be the current active lord.
looks like gustang and the top tower has different plans for Viole the irregular. they want viole to get stronger than zahard because zahard and 10 warriors were unable to pass the guardians test themselves. so they gave him the thorn via FUG because they want him to advance to the 135th floor so, that they can go there too. like FUG they must also have been waiting for someone to climb the tower's final floor and viole is their answer too like FUG.