Hi Nathaniel !! Welcome to the forum - you came to the right place!
In the USA, any kid under the age of 18 can build any size rocket - Kit or Scratch-built - no membership, no certification required. All you need is a little "rocket-building-skill".
Flying the rocket is another matter...
When you are under 18, you can only buy and fly single-use rocket motors that are "F" power or less. No reloads, and nothing bigger than "F"
.... unless...
...You join a national organization - Like Tripoli or NAR. Joining one or both organizations is the best way to learn about and participate in High-Power rocketry.
Under the NAR rules you can fly the rocket you build on an H or I motor with the help of a High-Power certified adult. This gets you a Jr level 1 certification.
With Tripoli, you will take and pass a written test to achieve "M" certification, which allows access to the High-Power area at a Tripoli Launch. Fly your Rocket on H or I power with the help of your Tripoli "Mentor" to achieve "M1" status.
You can find all the details at the
Tripoli or
NAR websites. Better yet - attend a club-sponsored launch in your area (non-member spectators are welcome) and see, ask questions, and learn first-hand!!!
Hint- most rocketeers love to talk to newcomers and spectators at a launch - they might even have some low-power rockets for you to launch. !!! Score-Win-Bonus !!!
Here's a photo of me with my Jr L1 and M1 Rocket.
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