Our Terms of Service currently require that the party who books on Hipcamp needs to be of legal age to enter a contract. This may vary by location, so it's important to understand those terms ahead of time.
However, as a Host, you're more than welcome to set your own policy regarding age requirements. If you prefer that Hipcampers be above a certain age to book at your property, simply put that requirement in your property or site description.
For more tips on what to write in your description, check out this FAQ: What should I write in my site description?