Twenty-one or over, guests and therapists alike
Everyone who books and everyone else in the room has to be twenty-one or over, which is why a photo document may be looked at briefly at the door.
The rule applies in both directions and it does not bend. Every therapist on the roster is twenty-one or over. So is every guest who books, and so is anybody else who will be in the room when she arrives.
The four seconds at the door
She may ask to see something with a photograph on it, which takes about four seconds. A glance, and the document is back with you in a second. Nothing is copied, nothing is photographed and nothing at all is written down. For a guest who has asked for a quiet visit this is worth knowing in advance, because it is the one exchange at the door that will happen regardless, and knowing it is coming removes the small jolt of being asked.
When she cannot be sure
Where she cannot establish that everyone present is twenty-one or over, she leaves without starting. That is not a judgement about anybody; it is the only workable response to an open question, and it applies to a second person in the room as much as to the guest who booked.
Where the rule is written out
The age statement sets it out in full, including what she does and does not do with a document she has been shown. The terms restate it in colder language as one of the conditions of every booking. Nothing on this site is intended for anyone below that age, and no part of the roster or the writing here is arranged to be read by them.