They've survived. Humans can survive terrible things.
> I'm assuming that, because they have lived in such a closed ecosystem for so long, they have different diseases than we have.
Not really, because their ecosystem is not closed. Birds and fish and so on still bring parasites, insects fly around, and malaria is malaria wherever you go.
> I'm also assuming that for the diseases and medical conditions they have, they probably can find medicinal plants in the forest.
But not good ones. We've never once found plants which make anything nearly as good as penicillin, and there's no reason to expect that we ever will.
> I doubt however they have the same life expectancy as we do!
And they may well have to practice infanticide, and/or go on bloody campaigns to keep the population down low enough they don't starve.
Looking at their advanced weapon technology I would guess that they are very warlike, and have regular tribal wars.
I'm the first to admit that I probably wouldn't last a week there. It seems quite romantic, living on a deserted island, without the antics of our society. But gathering food and water is hard, or even near impossible for us. These people however, seem to have found a way to survive.
I'm assuming that, because they have lived in such a closed ecosystem for so long, they have different diseases than we have. I'm also assuming that for the diseases and medical conditions they have, they probably can find medicinal plants in the forest.
I doubt however they have the same life expectancy as we do!