Several US states now require age verification for adult content (I don't know how that is defined). A case challenging such laws is being considered by the US Supreme Court, but most experts believe the court will allow the age verification.
That may mean users identifying themselves, which seems dangerous. (It should not at all be dangerous, but it is.) All you need is some phobic government official to sue or investigate you, for any reason they can come up with, and demand all your records as part of their lawsuit/investigation.
Perhaps there's a way to do age verification while minimizing privacy risks? For example, verify their age, give them their credentials, then delete the PII? I don't know if that would suffice if your age verification practices were challenged.
(Talk to an expert.)