Ooops, no not solved at all. That was a sanity test to see if the avatar could teleport to the island.
I've reset the group rights on the parcel so teleport failing again.
I'm not sure I understand the maturity rating issue as we've not had a problem before and no avatars have had to prove their age.
Either way, I've removed 'moderate' for this parcel and teleport still doesn't work.