Is there an age limit on participants?
Not directly. If you are sufficiently in control of your own life that you can guarantee that you’ll be able to dedicate the day to it (this applies as much to anyone who is married as to participants who live with their parents), and your writing is of a sufficiently high standard… sure.
Basically, I’m not going to ask your age. By volunteering to take part you are self-certifying that you have all necessary permissions to read the kind of material that will be produced. There will most likely be some grisly parts.