My lemon trees are around six year old. These trees are not giving any fruits so far.
No Fruits From Lemon Tree
Certified GKH Gardening Expert
I would try giving it some phosphorus rich fertilizer, like bone meal. If it is lacking phosphorus, it will not be able to produce blossoms (which means no fruit.)
The requirements for lemons are very similar to that of limes. If you have not read it yet, this article may also be helpful: https://www.gardeningknowhow.com/edible/fruits/lime/reasons-and-fixes-for-lime-tree-not-producing-blossoms-or-fruit.htm