Can a man get hereditary alopecia at a young age if his father has not lost hair till about 50 or older?

Yes: Everyone's genetically different (well, just about) since your environment will also affect how your genes present themselves. My point is that it's quite possible for someone to lose their hair earlier than everyone else in the family. If it's typical male pattern baldness, we can offer Finasteride & Minoxidil to try to slow down loss. But beware of side effects like gynecomastia, etc.