Rumor has it that the tree has to feel old enough before it actually bears -- as in, it doesn't really matter how old it is, it likes to wait for a few years and 'few' can be 'many' if it's not ready.
Weird, huh.
I don't know how old this one is, so I'm pollinating it myself with a tiny paint brush just in case this is the year it decides to make lemons. I brush all over the sepals and then the pistil in the center of every blooming flower. Then I go back and do it again so that everybody is getting someone else's pollen.
I hope it works.