In the movie, it is stated that he threw the Rasengan and was able to make it vanish and reappear. Also while watching the movie, in one of his fights in the third match, he was in the form of the Hyuga's family Gentle Fist's way. At the point in the movie where he throws the Rasengan at the Hyuga's member, he had made it vanish to reappear and explode.
How is it possible at his age?
Boruto has the Hyuga blood within him therefore he has been trained in the art of the gentle fist by his mother and grand father. Being a prodigy he has already learned it.
Boruto's Rasengan is not like Naruto's Rasengan. Boruto accidentally added added a change of Nature transformation along with the change of shape transformation needed for a pure Rasengan. This makes his Rasengan more like Naruto's Rasenshuriken. But unlike Naruto's Rasenshuriken which adds the wind element to the Rasengan to transform it into a shuriken and attack the target, he subconsciously adds Lightning Release to it resulting in the technique disappearing from sight.
I believe that Boruto doesn't have the gentle fist. You guys say that Boruto has the gentle fist because his gale palm has the same concept as the gentle fist. With Boruto's gale palm he makes wind element come from his palm and it looks very similar to the gentle fist but it's not. If your like oh he can see charka points, well his jougan can see charka points, portals and many more things. Even if he can see the points he can't really do the gentle fist because in the hyuga fighting style they infuse charka into their hands meaning Boruto will have to learn the hyuga fighting style and infusing charka into his hands. Now I remember seeing one person say that he got trained by his grandpa and mother in the hyuga fighting style. I believe that that's false because he seems to be using a fighting style very similar to that of Naruto's.
For Boruto's rasengan, Boruto has done 5 different rasengans so far in the anime. The first one he made is the vanishing rasengan which is when he adds lighting element to his rasengan, and he does so without knowing. The second one is when Naruto helped Boruto do a very super big rasengan simliar to the super odama rasengan. The third one he has done is the normal rasengan which you all probably know about. The fourth is Boruto's wind style rasengan which is different to the rasen-shuriken because the rasen-shuriken is basically more of a shuriken then a wind style rasengan. The fifth one he has made is the high compression rasengan(since boruto didn't have vast amounts of charka that Naruto did he couldn't make his rasengans very big. So what he did was compress his rasengan to make the impact even stronger.)
