Hey everyone!
Michael, Editor in Chief of Tapas here. I just wanted to chime in about the 18+ rule.
As others have pointed out, there are a lot of legal constraints that we have to abide by for any type of paid services that we offer on Tapas. Federal and tax regulations, domestic and international labor laws, the list goes on and on in regards to all the liabilities that we expose ourselves to without this rule.
But there are also other pragmatic reasons for these types of rules. For starters, writing a book takes a lot of work, and we try to establish a consistent and manageable pace of work so that we can publish it in a timely manner. It's a bit difficult to ask for minors to commit to these when they often times have other (arguably) more pertinent obligations such as academia or extra curricular activities. We would also need parental consent and legal binding contracts which as @Rodimus13 mentions are difficult and often times rather awkward to enforce.
While I would love, love, love to open up the Writer's Camp to more writers of all ages, these limitations make it almost impossible for us to attempt it. We have discussed internally other options in the future, such as scholarship prizes for those that are underage. Maybe this is a good alternative to meet writers like yourself halfway.
I apologize for the circumstances and hope that it doesn't dissuade you from writing. I look forward to reading your work, and who knows, maybe I'll be your editor in 4 years. Here's to hoping. Best of luck!