This is a doujin side-story of the series Miman Renai, both of which are done by the original author Takashima Hiromi. The series is about a 29 year old programmer for an eroge company who meets a 13 year old middle school girl one day by accident, and winds up falling in love with her. Despite the way it sounds, it is a very pure and cute series, and I highly recomend it.
(PS, there IS one of the bonus pages at the end of the doujin where the guy's boss (she's the same age as him) flashes him, but I didn't think that one panel kept it from being non-H. If people disagree, let me know and I'll change it.)