In The Name of Allaah The Most Merciful, The Ever-Merciful.
All praise is due to Allaah and all peace and blessings be upon the Messenger of Allaah, sallallaahu ‘alayhi wa sallam.
There is a morally perverted young man who is an addict. If we give him his share of inheritance, then surely his aberration will increase. Is it valid under sharia to give him his inheritance in the form of a monthly salary until Allaah Sets right his affairs?
May Allaah Reward you.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

The ruling of giving money to a foolish person applies to the mentioned young man because he wastes his money in ways that contradict sharia and sound reason by spending it in unlawful matters that are unanimously regarded as reprehensible by rational minds. It is impermissible to enable any such person to have his inheritance or any other money. Allaah Almighty Says (what means): {And do not give the weak-minded your property, which Allaah has made a means of sustenance for you…} [Quran 4:5] until Allaah Almighty Says (what means): {Then if you perceive in them sound judgment, release their property to them.} [Quran 4:6]

So, withholding money is conditioned with having sound judgment. Anyone who spends money in drinking liquor and other sins definitely does not have sound judgment. Ibn Al-Munthir said, “Most scholars of the nation from the people of Hijaaz, Iraq, Ash-Shaam and Egypt see that every person who wastes his money must be restrained, regardless of his age.”

Ibn Qudaamah, may Allaah have Mercy upon him, said, “Most scholars said that sound judgment is to spend money in a righteous way. If a person spends his money in sins like buying alcohol and devices of entertainment or to achieve corrupted goals, this person does not have sound judgment because of wasting money lavishly without any benefit.”

It should be known that the father is to be the guardian over the foolish person’s property. If the father is not available for any reason, then the guardian is the person who is appointed by the father before his death. If the father of that foolish person does not state in the will who should be the guardian over the property of that person, then the ruler should appoint an honest trustee or the ruler himself or his deputy should be the guardian. If there is no ruler or if he is dysfunctional, then a trustworthy relative of the foolish person or any other trustworthy person should be a guardian over his property. This is the ruling in case of permanent foolishness. If such foolishness is new to that young man, then the way for him to have his property at his disposal under guardianship is through the judge because proving foolishness requires investigation. The judge is the only person who can decide this case.

So the questioners should follow the mentioned steps. If it is agreed upon a person to be a guardian over this man in his spending, it becomes permissible for the guardian to dispose of the money in the right way, whether in the way mentioned in the question or in any other way.

Allaah Knows best.