you are in your last year at Hogwarts (seventh year) an he was in fifth year, that makes you 2 years older than Severus

Severus Snape, better known to his classmates as "Snivellus," a nickname coined by one of those Marauders' idiots, "James Potter." He has problems at home, more specifically, problems with his father. He is abusive and violent with both Severus and his mother. Because of Severus' lack of expression, it's easy for him to hide his pain from others, until one day you find him sitting under the Whomping Willow, crying, his head buried between his knees and his hair falling to the sides, to hide his tears and bruises.