Is it permissible for the guardian of an orphan's wealth to take a percentage of its profits in return for his work, and is there a specific percentage for that?

If your brother reaches the age of sixteen, he is considered an adult, and it is not permissible to dispose of his money except with his consent, unless he is a spendthrift or mentally incapacitated. If he reaches maturity, his money must be handed over to him, based on the Almighty's saying: "And if you perceive in them sound judgment, then hand over to them their property." If you took the money for trade, all the profit belongs to your brother. If you gave it to someone else, he is entitled to the profit that you both agreed upon. It is permissible for a poor guardian to consume from the orphan's money in a reasonable manner.