As per the laws of Saudi Arabia, your case falls under periodic rights, which are covered under Article 83 of the Saudi Lawsuit System - "Without prejudice to regulatory texts, the denial is not heard after the expiry of five (5) years in the following rights: B- Periodic renewable rights, like rent of properties, salaries, and fixed revenues, and the like."
This would mean that a school can technically bring a case forward or send a legal notice to a fee defaulter at any point within 5 years after the default. After this 5-year period, the school may not legally be allowed to bring forth a complaint or send a legal notice.
In practice, this means that if fees have remained unpaid for a period longer than 5 years, a school may no longer have a viable claim against the defaulter. However, it's important to keep in mind that laws can have different interpretations and outcomes can depend on various factors.
Additionally, please check your contract or agreement's specific terms with the school. If an alternative dispute resolution method or specific time frame for action is provided for unpaid fees, you should adhere to it. It's always important to maintain good record keeping of notifications, warnings, and communication with the defaulter in case you need to pursue legal action.
Please consult with your local legal council to ascertain the most accurate guidance given your specific circumstances.