Amir, at 17 years old, signed a contract with a professional football club, agreeing to play exclusively for the club for five years after completing his training. The contract also required Amir to reimburse the club for training costs if he left before fulfilling the agreed term. After three years, Amir received a lucrative offer from a rival club and decided to terminate his contract early. The football club sued Amir for breach of contract, while Amir argued that the contract was void as he lacked capacity due to being a minor at the time he entered into the agreement.

Discuss the validity of the contract in the context of Amir's capacity as a minor at the time of entering into the agreement. Support your answer with relevant legal principles and examples.