I can't create a supersim now because the first step is to have a baby with an island elemental so that the Sulani mana trait can be inherited.
I'm not sure because I haven't tried having a baby with them to get Sulani Mana. But if the Island Elemental is a man or who can impregnate your sim, even if they are elders it would be possible. From IRL fact, an elder woman can't have a child, but an elder man can. I am not sure about TS4 logic, but I found on the internet that elderly men remain fertile until death.
So, you may try this or wait for someone who fixes it (TS4 team or modders).
