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 your property, simply put that requirement in your property or property/unit description.
For more tips on what to write in your description, check out this FAQ: What should I write in my description?