He is very elderly and possibly blind. He is 4000 years old as stated in Four Monsters And A Funeral.
He is mainly shown playing video games, however on some occasions he helps Mavis. Like when she asked him if Aunt Lydia had any friends or if there is a mirror for vampires, even when she rushes out of the room before he tells her the down side of his advice. Gene doesn't like seeing his niece being hurt by her own reflection or by a large, cursing mummy while trying to defend one of her friends.