I friggin read this like idk earlier this year (2016) or late 2015 but ita about a girl who runs a bookstore or something and she sees this handsome guy and she falls in love with him but he's younger than her. It's a really cute story and I never saved it...

Halp

Well, the rest of what you describe sounds like Futari no Renai Shoka, though it's classified as Seinen rather than Shoujo.

Good luck 🙂