The key word in your question is underage. You can't.

Don't do it, the lack of testosterone will cause you problems you probably did not think about - being low can cause depression, muscle aches, joint aches, insomnia - look up  "low T" symptoms, and you could get all of them.

Being "gender neutral" is the least of the effects your orchiectomy will have on you.

You will also be asexual whether you wanted to be or not.

And you will also be without the hormone testosterone---which will result in all sorts of undersirable effects in your body, now and in the future.

Don't do it, the lack of testosterone will cause you problems you probably did not think about - being low can cause depression, muscle aches, joint aches, insomnia - look up  "low T" symptoms, and you could get all of them.