How does Ibn al-Qayyim permit a man to masturbate with the hand of a young girl or a non-Muslim woman who is not fasting if he fears the rupture of his bladder or testicles during Ramadan?

Enjoying a young girl has rules and details, and what Ibn al-Qayyim mentioned is not problematic, for enjoying a young female slave or wife is permissible as long as it does not harm her. If it harms her, it is not permissible.