Is the book "What is Permissible and What is Not Permissible in Marrying an Elderly Woman," attributed to Sheikh Abdul Aziz Al-Rajhi, authentic, and what is its content if it is?

The attribution of the aforementioned book to the Sheikh is questionable due to its absence from accredited sources. The claim that Muslim scholars only think about sex is a baseless lie; rather, their discussions about the etiquette of marital relations clarify what is permissible and forbidden, and protect young people from prohibitions. The Salaf (early Muslims) used to avoid mentioning these matters in their gatherings, and the Prophet, peace and blessings be upon him, forbade the disclosure of marital secrets, likening one who does so to a male and female devil who satisfy their desires while people watch. The West is more deserving of this description due to their call for sexual culture without restrictions. You should advise your brother by explaining the seriousness of abandoning prayer and revealing his misconceptions, and seek help from people of knowledge.