are they grafted or grown from seeds? if grown by seed they take a long time to bloom. if they're grafted, then maybe some fertilizer.

Yours are big enough to flower, so I have a question for you. Do you water them? The trick to getting mangoes to flower is to allow their roots to dry out. Mangoes are extremely drought tolerant and need a couple of months of dry before they will bloom.
I 'prune' by cutting out the center vertical in the late fall or winter, and leave 4 or 5 main branches spreading out. Not necessary until the trees are taller, but I prefer my trees to be 25' or less tall. And lower is better come harvest time.

This is a pic of a mango from my keitt this past summer. I planted the tree at the beginning of spring, the tree was four feet tall, and it bloomed nicely. I had several mangoes, this pic is the largest one. It was delicious and easily sliced because of the thin seed. I use mushroom compost, rabbit manure, chicken manure, and leaf compost. I would also like to mention that my Keitt is now starting to bloom and its December! I know the weather has been unusually warm the past couple of Weeks but I thought the tree wouldnt bloom again until around April or May. rsmith28hi@yahoo.com

This post was edited by 407Bob on Fri, Dec 14, 12 at 21:38

Most of my Keitt trees have fruits now. At least one of the trees has fruits that are larger than 1 pound size, although it is just the month of June. The next time I visit my farm, I will get some pics and post them here.