Actually, shoujo are all about love, it's the main subject, whereas in a shonen it's something in the background of the main story, or at least it's secondary.... Usually there's not much love in a shonen, it's a quite recent phenomenon to add important love stories in them (in Sword art online for example), and there are also more and more anime/manga that don't really fit in a category (to me), like Haruhi Suzumiya or Lucky Star, soooo.... Well, actually Toradora can be considered as a shoujo, but you're right, it's not particularly aimed for girls because I think anyone could like it.... Anyway, the original work is a light novel, I just checked xD