First, he is 21.
Second, we do not know what the fight was about.
Third, CCC# 2230 states:
When they become adults, children have the right and duty to choose their profession and state of life. They should assume their responsibilities within a trusting relationship with their parents, willingly asking and receiving their counsel. Parents should be careful not to exert pressure on their children either in teh choice of a profession or in that of a spouse. his necessary restraint does not prevent them - quite the contrary - from giving their children judicious advice, particularly when they are planning to start a family.
Fourth, I do not know what the “issues” are between his mother and grandmother, and I don’t think it is any of my business. I have to wonder if the mother is the one who is the controlling one, unless there is something truly “toxic” about the way the garndmother acts. Besides, I don’t remember if the OP said, in either this thread or his other threads about moving, whether he would be staying with his grandmother or not. Either way, I really honestly think it stinks rotten when the chldren - no matter what age - are caught in the middle of and are used as pawns in family squabbles.
Fifth, it is interesting that he did not mention what his dad thinks about this situation.
Personally, as long as you are knowledgeable about and practicing your faith, I personally think, as a “big brother” in Christ, you really honestly need to get out on your own. If you want me to elaborate, I can PM you.
By the way, did you ever make it to Mass today?