Okay, I tried this with a different Sim - one who wasn't an elder.
I'm building an animal sanctuary (wolves, skunks, haven't managed to catch a penguin yet but it's only a matter of winter coming I hope!) and I caught a wolf with glowing eyes called Bailey and added him to my wolf enclosure. Worked out I needed to remove the gate as no matter how I locked it, come hometime for wolves he would just get up and try to leave.
I used boolProp to increase the relationship bars to 100% for both the Sim and the wolf, and he bit the zoo keeper the very same night!!!
Now I suspect that elders might not be able to get bitten
