Thank you, thank you, thank you, Ciraarana, for this wonderful story!
It is really amusing that you tried to write a short story, but Severus wouldn't let that happen. What you ended up with was even more perfect, and just the type of leisurely unfolding plot that I adore. You have a great way of creating an atmosphere 'outside' all of the demands of the wizarding world. It allowed Harry and Severus to redefine their relationship without all of the animosity of their past.
I like how you handled the de-ageing; it was logical, the magical theory was plausible, and it set up situations in which Harry had to protect Severus--something that I loved! Harry trying to get Severus to take a shower was hysterical. You wrote such an endearing, infuriating creature--he could only be a teenager! Harry was in the difficult position of trying to parent someone to whom he was attracted, who was also underage. And, even in letters and as a teen, you managed to keep Severus's snarky attitude and comments. They were such a delight.
The sex was hot. Severus seducing Harry was delicious, and Severus 'topping from the bottom' was just what I would expect of our demanding little teen. Severus learning about sex from a book was just too, too cute, and so Severus.