What if time moves so slowly on the island that (just as an example) 1 day on the island is 10 year outside of it. That would make anyone on the island practically immortal. Thus the reason "the others" stay there and do everything in their power to hide their secret.

You could push the idea even further by looking at the theory of The Others being the children of the Lost. It all makes perfect sense and could explain a lot of the things happening on the island.

Polar bears? If the time warp theory is correct the polar bears could have lived forever on the island from way back in the ice age. The babies and the corporation, it all makes logical sense.

Realistic? Hardly. But either is Desmond seeing the future and a priest being attacked by polar bears on a supposedly random island.