We had several do the same thing, seems it was to hot and dry. They are at the peak when dark, almost black, but I like them when they just start to turn a dark brown. The flesh is more firm, refrigerateing them helps. We have sit green one's in the window, or put them in a brown bag for a few days and they do seem to ripen OK, but not like on the tree. I have to fight the deer, coons and opossum at rippening time, the coons and opossum climb up the tree and break out the top or small limbs. I think we now have around 100 trees or so, some wild, some I transplanted, some from seed. Very young trees seem to be eaten by beaver or muskrats that are along the creek. The Indiana banana is very good to eat, some websites claim they fight or stop cancer, do a google search, very interesting. BEAR