... as others have said, Gabe's dialogue is sometimes too mature and that is distracting.
... and his narration is simply too prevalent. Not every scene needs Gabby Gabe's relentless commentary.
Other than that, I thought it was a little gem of movie.
That's exactly what I thought the whole time. The kid who played Gabe was kind of charming in his own ways, but the very mature narration makes the movie a little less charming.
It's obvious the screenwriters were writing in their own, adult perspective, which to me makes the movie less realistic.
But like you said, overall, the movie was good, I enjoyed it.