Awww, this is utterly sweet, and what a genius idea to change their ages around like this! I just love your Viktor -- and Severus's lively apprehension of his fellow Slytherins and their unpleasant ways of expressing their displeasure. Also very cool, the way Severus gets a glimmering of Harry's bad home life, and we see a bit of Severus having to scheme and work to get ahead himself. This is a great AU!