Age differences are pretty icky, may be triggering to people who have had similar experiences. Although this story does go a lot better than real relationships between adults and minors, it's still gross to read.
If they had been aged up to at least high school and uni the age gap wouldn't bother me so much. 13 and 19 is grim, 18 and 24 isn't so bad. If you can get past that the story is nice enough but I'd suggest reading Honto Yajuu instead if you like this author.