No, it's not housing discrimination. A landlord is free to decide who to rent to--and who to not rent do--for any reason not specifically prohibited by law. There is no protection, however, for "college-aged people": a landlord may choose to "discriminate" against you by not renting to you, such a landlord could refuse to rent to Trump (or Hillary--take your pick) supporters, or cosplayers, or people who work the night shift, etc.