I've done it as well with my parents, who love wine. At the shops I've been to, you buy the grape concentrate up front and they handle to process of making it up until bottling. Once the juice has fermented, you go in and they walk you through cleaning and sanitizing the bottles, filling them, corking them, and usually shrink-wrapping the tops. They provide all the supplies except the bottles themselves - customers bring their own, saved from buying wine the "normal" way.

Never seen a shop do ageing, so the wine will be noticeably "young". My parents like dryer and sharper white wines anyways (Pinot Grigio, Riesling, etc.) so it doesn't bother them. Also note that due to taxes and such, the cheapest wine you'll find commercially is C$11 a bottle, so even at C$20 / gallon you're getting a great deal if you like the resulting wines.

Personally, I quite like the wines my folks get through these shops - properly chilled they make a wonderfully refreshing beverage in the summer, and we'll often drink a few bottles on the back deck together when I go to see them.

It's only Canadian money. :-) <$16 USD