If Atom is indeed depicted as an adolescent, it would seem indicative of the screenwriters' lack of background into Atom's manga history. In his preface to Egyptian conspirators, Tezuka wrote that when he depicted Atom as older, the series' popularity dropped. In fact, the popularity seemed to vary inversely with Atom's age (to a point, anyway). Both Goku & Arale are strong as titans, but their creator Akira Toriyama makes them as cute as they can be.
I think with this film the idea was that little kids would not appeal to American kids who are in a hurry to grow up as much as older ones would. 
