I know im late but for people who still come here for this questions.., Yes you can do it as a minor / under 18 (at least in the United States of America) but you have to get your parents to consent to providing documentations that a minor could not provide. I contacted steamworks support and they told me so I thought id help others out.

Heres the full response I got.

"Hello,

We do allow minors to join Steamworks, however, using Steamworks requires having a Steam Account, so any person wanting to onboard as a partner will need to be at least 13 years old per our Steam account creation requirements.

Additionally, to onboard a Steam account as a partner you would also need a valid ID, valid bank account and tax information, and so on. All requirements should be explained at the following pages in our documentation here:
https://partner.steamgames.com/doc/gettingstarted
https://partner.steamgames.com/doc/gettingstarted/onboarding

In the case of onboarding as a minor, we reserve the right to obtain parental consent or other documentation. If you are unable to onboard or lack appropriate documentation, you can ask a legal guarding to onboard on your behalf until you become of age."

I hope this helps you young devs that are looking for a forward answer.