Thanks for your question. Are you in Mauritius? What type of lemon tree? Could you please send a picture of it and the leaves? Thanks!

Hello, thanks for your response.
Indeed, I am from Mauritius. I am sending you pictures of the lemon tree. Thanks for your advice.

Thank you for the photos, Mr. Perne.  It does indeed look like a very healthy tree, and since it's over 5 years old, the cause of it not blooming is not because it's not mature!  I wish I could provide you with some information from an academic source, but I'm afraid the best I can do is a link to a short article about this problem, and lemon trees' needs.  I'm especially interested in whether you have been fertilizing it with enough phosphorus (phosphate) and potassium (potash).  Its healthy foliage would indicate it is receiving lots--perhaps too much--nitrogen, which promotes green growth.

I also cannot tell whether you have been pruning your tree, and, if so, inadvertently removing the buds on the ends of the branches, which eventually mature into fruits.  You don't indicate whether you have seen any blossoms on the tree, so blossom drop might be analyzed.  

I would urge you not to remove this tree until you have had at least 2 seasons applying the nutrients (phosphorus and potassium) as suggested by this article.  Let's hope it has just been a nutrient deficit; it would be a shame to lose this magnificent plant!  Good luck!