Mike,
I will not doubt anything when it comes to trees. I get suprised all the time. Trees are like people, some of them will bear fruits earlier and some of them will not bear fruits at all.
Example, you grow one tree and supply the tree with food, water, warmth, care, medicine, and so on. On the other hand, you plant another tree and let if fend by itsef. You don't give it anything, nothing! The outcome will be different!