Board Thread:Spoilers!/@comment-27060727-20180222230337/@comment-25926288-20180428223505

Begfhn wrote: I've had this theory for a while, and now it's almost been confirmed. I wasn't sure whether or not the 2017 thing for this season was a mistake, but now it appears it isn't. The curse sent everyone back in time. In Storybrooke, only 3 years have past since the end of last season and there is a 16-year-old Henry. Henry needs to somehow get help from his younger self without messing up the timeline. Adam said/implied as much in Twitter because fan asked some question and Adam said that Henry did graduate (which is 2018/2019 school year) and how it was 2017, he said will be explained. (And I believed him in that because he reinforced that it was 2017 in HH.)

A good chucnk of isers believe that the curse travelled to the past.