Futari no Renai Shoka

Kanako is a young woman who is running an old book store. One day, a customer comes in who shares her taste in books. He's a teenager named Akio, and he and Kanako quickly find that their taste in books is only the first of many ways that they fit together well. Kanako immediately realizes she wants him, and soon blurts out awkward things, like proposals of marriage and cohabitation. Despite their different ages and their awkwardness, it seems like their relationship has the potential to grow into something beautiful.

(Source: MangaHelpers)