How can one deal with a 15-year-old boy who sits and mingles with non-mahram women (mother, sisters, his mother and his sister) under the pretext of his young age, and what are the limits of advising in this case?

If a young man reaches the age of fifteen, he is considered legally an adult, and he must be prevented from mixing with women or entering upon them without a mahram, because he has become a source of fitna.

He should be gently and kindly advised of the necessity to stay away from these forbidden practices. If he does not respond, then he must be prevented from entering upon women.

The mother and sister must also be advised of the necessity to stop this negligence and forbidden mixing with him.