Within the experience editing form, you have the ability to set order limits, both minimums and maximums for the total order quantities.

The Max setting limits the customer from adding too many bookings for an experience to his or her cart. For the minimum, the customer cannot proceed to checkout or complete a booking without enough selected.

These limits apply to the total order, not to the individual variants (on experiences that have variants). A typical example is that you set a maximum of 5 tickets. The customer wouldn't be able to reserve 2 adults and 4 children (6 tickets) but instead would be limited to some combination of adult and child that is 5 or less.

You can find this setting in the Payment section of the experience when in edit mode.

Once you click "Edit", you'll see this where you can set your limits.