Are there sound and authoritative proofs that frequent recitation of the Qur’an protects against senility (aging), and if so, what are they, and how can sincerity be achieved in recitation so that its purpose is not to preserve mental health but to please Allah?

Reciting the Quran is a great act of worship. It has been reported in some narrations from the Salaf that reciting the Quran is a cause for protection from senility, and that whoever recites the Quran will not be returned to the most decrepit stage of life. A person who is diligent in reciting the Quran will not suffer from senility or delirium. The intention here is that a knowledgeable person will not reach the senility of common people. If you recite the Quran sincerely for Allah Almighty and intend to be safe from senility, this does not contradict sincerity.