I can only speak from the AF side, but 21 is their limit for a curvature or was in 87.
Have you seen a specialist? If not I would go to one. Scoliosis curves can vary just by breathing at the moment the xray is taken.
I know you think it doesn't matter, but the problem/dangers associated with scoliosis is the impact of your internal organs. Bullet''s sister, and his niece both have had scoliosis operations, so our family knows a little bit more than the avg bear when it comes to this.
Bullet 6 weeks prior to commissioning with a rated (UNT) slot was dqd. because he had a 23 degree curve. His folks to him to his sister's surgeon, and had him test him. The curve was 19 degrees according to that doc. The doc happened to be the 1st doc to ever perform the scoliosis operation in the US, written up in magazines like Time, People, etc. It was hard for the AF to say that the number 1 doc in that specialty knew more than the flight doc that gave him the physical.
To this day Bullet believes it was that action his folks took that made sure he didn't get DQd. He served 21 yrs (ejection seat airframes) and it was never an issue again.
Good luck.