My Eureka lemon tree this year is producing small lemons. The tree is 7 years old. I feed it and water it regularly. I live in Australia.
Certified GKH Gardening Expert
Your tree may have too much fruit. Fruit trees only have so much energy they can dedicate to their fruit, weather that be 10, 50 or 100 fruit. The fewer fruits on the tree, the more of that energy is dedicated to each fruit. Citrus trees typically self-thin, but sometimes, they need a little help.
Next year, if you see an unusually large number of fruit developing, try removing 1/3-1/2 of the fruit.