Thank you for a great read (which I shouldn't have, until tomorrow. Ah well). First and excellent! Here you've given us a good way of getting an acceptable age difference, and of giving Severus a better life, and of knocking Voldemort off without almost breaking the wizarding world.
I like your adult Harry – he still has impulses, but he manages to control most of them, and he thinks – and he's emotionally mature. Your young Severus is very believable. I'd love to see him as an adult, with experience of life, too.