Becky is 23 still living home and still gets a spanking if she really deserves one as does her 19 year old brother.
These spankings not only emphasize your authority, but also build his stamina, while releasing pleasing endorphins in his mind, which help him learn to associate pleasing and obeying you with both pain and pleasure.
So he always knows, week to week, exactly how Melanie has been behaving and what aspects of her behavior he most needs to address.