I think he started in middle school after finding a book about it in the library, because you get into all kinds of shit when you're 14 and have no one really watching you. He made moonshine in his sink and it turned out awful. But that only made him more determined to make it work and after a while he got good enough at it that he started wondering if he could turn gummy bears into wine.

The rest is history.

And of course Mephisto dragged him into it. B( What does Shirou look like to you, a geek?