I thought it was pretty good for a first time.
With the interviews try not to have them right in the middle. Get closer to them so its not their whole body in the frame. Next time maybe try having them more to one side of the frame (doesn't matter left or right its up to you.) and then you should sit on the other is of the camera so the person you are interviewing looks across the open space at you. I found they were kind of looking around and stuff while they were talking it was a little distracting.
With the kid in the red you had him sitting with the sun at his back. If you are going to do that maybe try having a flex fill or bounce board (Something to reflect the light) so you can fill in the shadow on his face.
When interviewing outside try to do it on a day with no wind at all or maybe invest in a deadcat to help with with wind clipping.
The editing was good, but i think you could have had some more b-roll over the interviews like where there are jump cuts in the interview. (2:50 for example)
Do you have a good tripod? If not i think that might be the next thing you should look into getting. Felt like a few good tripod shots of them skating could have added a lot to it.
I think thats all i had to say. Well done tho! Documentaries are pretty fun to make.