Neem tolerates pruning very well. That's why I mentioned that you can top them off, leaving about 12' of remaining tree, with a few branches with leaves to support what's left, and taking all of the branches above (normally 2" to 4" in diameter, and 10' to 20' long) for use as fenceposts, or charcoal manufacture, or just plain wood. The branches will regrow in two or three or four years, and you can do it again and again.
IF you give the tree water, it will grow very quickly in the early years. Later, when mature, if you stop giving it water, yes, it will then grow about 2' a year from then on. During the rainy season, there is no reason to water, but it does help the trees during the dry season.
I am no Johnny Appleseed, but I have contributed a few hundred neem trees to the earth's environment here in the Caribbean, and lost none once they were in the ground. I started all from seeds in 6" pots, let them get up to 2' tall, and then transplanted them into the ground, with an earth ring of about 3' diameter around each one to hold the water I gave them. I also added some peat moss to the soil that I packed around their roots, in order to hold the water better, and to give the little trees a bit of a boost when they were rooting in the beginning.