What a beautifully-crafted story. There isn't an unnecessary word in it, and the characterization of both Aberforth and young Severus is brilliant.
There a so many great lines I couldn't possibly quote them all, but one of my favourites is Aberforth was old enough to want to smile at such a thing, and not enough of a knob to actually do it.. Sums up Aberforth's wisdom, as well as Young Severus.