Fairly solid writing, I felt, and a good opening. The characters felt pretty realistic and relatable to, as well as their reactions. I do wonder why he had not drawn the line earlier than twenty-one personally - would this be something you'll touch on later curiously? I also wonder on why the parents did not let him go, although my guess is being overprotective being part of it. And a trainer starting out as an adult is certainly a curious concept. I particularly liked the part about him observing his room as well - some nice description there. =)
I think it did somewhat grab my attention but I will agree with Misheard Whisper that it did feel a bit lacking in a way in that regard, and I am also curious to see how it follows given you named it a prologue as well. Perhaps it would have been a good time to have presented some more on what I mused about - why exactly had he been delayed by a whole 11 years, and why he wanted to go so badly (I am also on that note curious on what he was doing before then - always at home, or working in some other manner?) But that does as said depend on how you follow it up, but if you do continue with the next morning and all then making this a chapter would likely fit better instead, imo.
At any rate, good luck with the rest of your story!