Ah, that’s a good question. I personally am not a big fruit eater and I just about never try any new fruit, so I don’t know offhand. I believe it’s 12 months, but I can’t say that I’m certain about that, so please don’t rely on it. I’m sure someone else will know the correct answer to that question.
But the general rule is correct. Anything for which you would have otherwise made a Shehechianu can be used for the bracha on Rosh HaShannah.
The Wolf