The gemarah (Shabbat 33b) states that when Rabbi Shimon bar Yochai and his son Rav Elazar were hiding in a cave a carob tree miraculously sprouted from which they ate. How could they eat from this tree within the first three years of its growth, for doesn't that transgress the laws of orlah?
Another answer (suggested here in the Sefer "Kerem Efraim") is that because the tree was created through a miracle, it was not obligated in Orlah. He brings support from the Radak (Malachim Beis 100:4) who writes that the oil that was miraculously created for the wife of Ovadia did not require Maaser to be separated from it.
He explains that for the first three years of a tree's life, the powers of evil rule over it and this is the basis for the prohibition of Orlah. However, the Gemorah (Sanhedrin 59b) writes that nothing impure descends from heaven, and therefore the tree miracoulsy created for the Rashbi could be eaten from immediately.
In my opinion has said above, since this tree grew “al pi ness” there is no issur orla bound to it; also since it was fully grown -like a 4 years old tree, obviously a miracle- there should not be any issur. On top of it, if HKB”H sent these fruits to save their lives, He “managed” to give them some eatable stuff, and not any issur.