If all of them stopped bearing at the same time then I would guess it is not old age. They wouldn't all get "old" at exactly the same time.

Weather could be another factor. For example here in California we had a lot of rain last spring when all the fruit trees were in blossom. It washed off almost all the flowers and kept the bees away. So almost everyone had very little fruit. Don't know if the hurricanes could have done that but if the wind was strong enough and at the right time????

Also if you did any spraying (like the weed killer on your grass) and that spraying was at the time of flowering that might kill the blossoms.

Did any of the trees produce ANY fruit? Did the fruit never appear or did it appear and then drop from the tree before ripening? Was this the first year of non-bearing or has this been going on for a while (getting progressively worse?)

Thanks, Ken, I'll check the rainfall. They did have some blossoms but not as many as usual. The grapefruit tree has a little fruit on it, the orange practically none and the tangelo and lemon have nothing. Our lemon tree has been dripping with fruit for each of the 9 seasons we've lived here.

These trees were all planted at the same time. I don't know how long citrus trees live?