Is it permissible for a young man who is unable to marry and whose fasting does not quell his sexual desire, to increase his fasting by fasting without a pre-dawn meal (suhoor) or by delaying breaking his fast until the 'Ishā' call to prayer, due to the intensity of his sexual desire which has overcome his hunger?

Hastening the breaking of the fast (iftar (definition)) and delaying the pre-dawn meal (suhoor (definition)) are sunnah (definition) (prophetic tradition). Not doing so is not sinful, but rather contrary to the sunnah. It is sunnah to hasten breaking the fast once sunset is confirmed, based on the hadith (definition): "People will continue to be upon goodness as long as they hasten the breaking of the fast." It is also sunnah to delay the suhoor as long as the second dawn (true dawn) is not feared to have appeared. Hastening the iftar and delaying the suhoor can be achieved by a small amount of food or drink, and it is most complete by eating. For someone who finds it difficult to hasten iftar or delay suhoor, they can reduce the amount of food and drink between Maghrib and Fajr, and there is no sin upon them, but it is not recommended as it goes against the sunnah. They should supplicate to Allah Almighty, associate with righteous companions, and occupy their time with beneficial matters.