The fact that he is now an adult and the album for which he posed became iconic is immaterial.
He would have a better case suing his parents. But, as we all know, this has nothing at all to do with the photo, but about money that the album generated, and which neither he nor his parents had a share in.
I see no reason to settle this. He has zero chance of prevailing, an little chance that his case would make it to court, anyway.