Ruling 2270
A child who is not of the age of legal responsibility (bāligh) cannot legally (sharʿan) exercise discretion over his liabilities,[1] nor can he have disposal over his property. This is the case even though the child may be perfectly able to discern between right and wrong (tamyīz), take care of his wealth, and use it in a correct way (rushd). In this regard, neither prior permission nor subsequent authorisation from his guardian (walī) is sufficient. However, in certain cases, a child’s disposal over his property is valid (ṣaḥīḥ), such as his buying and selling of things that have a little value, as was mentioned in Ruling 2092, and his will (waṣiyyah) to his close relatives, as will be mentioned in Ruling 2714.
The sign of having reached the age of legal responsibility (bulūgh) for a girl is the completion of nine lunar years. For boys, it is one of three things:
1. Growth of thick hair below the navel and above the genitalia, [and on the face and above the lips (see next ruling)];
2. Ejaculation of semen;
3. Completion of fifteen lunar years.
Therefore, a minor cannot, for example, become a guarantor or take out a loan.