I've compiled an extensive list of reasons as to why I should be allowed to sign the NDA and become a Rivals of Aether beta tester
First, I will dispel some problems you had with this idea
1. Time- You said that there were more valuable things I should be doing with my time instead of devoting it to Beta. However, Beta would only consume the same amount of time that I'd be playing Rivals anyway. There is no obligation/minimum time investment required for a beta tester. Therefore it would have no affect on the duration of my study time.
2. Safety- I do not actually speak to any Rivals players vocally, and I do not stream. Therefore the only way I would be able to leak content is by:
a. Having it in the background of one of my videos, which exclusively shows modded rivals content and renders any potential changes indistinguishable
b. Conciously typing it out into a public forum and posting it, which is undeniably impossible to do whilst autopiloting. Additionally, here is a direct list from Beta about what I am and am not allowed to say, which reduces the ways in which i can break the contract even more: https://cdn.discordapp.com/attachments/377588235229986819/557012501708144670/Beta.JPG

As a result, it is practically impossible for me to break the NDA.
3. Age/Maturity- The majority of players signed in beta right now are in the 16-25 range, so I wouldn't be too out of place. I think that joining Beta would be a chance to prove my maturity and practice responsibility, which is doubly important when I'm going to be an independant adult soon.
Now for some of the benefits of me joining beta.
1. CV- Beta Testing experience is directly related to my desired field and is absolutely something that belongs to be displayed on a CV for someone who wants to be involved in software development
2. Skills- I would have to work with my other testers to test new mechanics and balance changes, and communicate with new people and the development team to give feedback and come up with changes. This enhances my teamwork, communication and problem solving skills which are definitely important life skills to have. Also note the maturity and responsibility I mentioned earlier.
3. Psyche- I don't need to tell you this, but I really do want to be part of beta because it gives me a chance to be part of something by doing something that I love. And I don't want to guilt trip you, but the last thing I need before my A level exams is to be forlorn about being denied beta access at the absolute last hurdle.
Finally, I'd like to say that next year there may not be a beta progran altogether, I may not be invited, or I may not be into the game by that point altogether. I can't afford to wait until I'm 18.

Between all of the points above, I hope that I can convince you that:
- The NDA is safe and reputable
- I'm mature and responsible enough for it
- it will be a valuable addition to my CV
- It will allow me to develop skills and grow as a more defined character.
Thank you for listening to my speech on why I should be allowed to sign the NDA. I hope I've managed to change your mind.