It happens gradually particularly once he gets over the girlfriend stage and settles down.
I never remonstrated with him, tbh I’m like that with both my children and it has paid off big time they are both so supportive and caring now particularly there like a shot if we are in any difficulty, like the odd heart attack, cancer etc?
We can absolutely depend on them now.
But to be fair we reciprocate - it’s called family.
I’m not sure that it matters how much rent you charge, it so much depends on your and their circumstances. Do what is comfortable. I never charged them anything, but we were comfortably off.