As many have said, it's really matter of taste. Most recommendations I've seen for both sexes is to go with making the scarf the same length as the person is tall.
But really, it kind of depends on how you want to wear the scarf, and how much of a "tail" or "hang" you think would look good on him.
Take heart that no one will be taking a ruler to your scarf, though! (Except for you yourself, lol). As long as it's long enough to hang like you want it, it's perfectly fine. (And, if anyone complains, well, they can make their own scarves then!)