Is fasting five days a week considered harsh on oneself for a young man unable to marry due to studying, especially given his recollection of the Prophet’s, peace and blessings be upon him, recommendation to fast for those unable to afford marriage?

There is no harm in fasting five days a week for whoever is able to do so. However, it is better to fast one day and break the fast one day, as the Prophet, peace and blessings be upon him, said: "The most beloved fasting to Allah is the fasting of David; he would fast one day and break his fast one day."