I started it from seed less than three years ago and then put it into the ground. Because it hasn't been pruned it takes the shape of a bush -- and that's okay.
It will still be a few years before it bears fruit. It just takes longer when you start them from seeds rather than grafting onto existing rootstock. I went the seed route because there aren't any grafted Key Lime trees available on Guam and also because of the storm potential. If a typhoon comes through and wipes out the top of the tree it will come back up true from the roots.