Do you know the exact name of the variety you have, or information on its growth rate, full size, and form? Have you fertilized it, which would encourage growth, or planted it in a fertile location? 

If it needs to maintain a central leader, it will need to be pruned differently than if it forms more of a ball. Limiting size will be tricky. Pruning cuts made after bud-set in the fall will encourage growth, resulting in a denser foliage with more shoots forming near each cut. You can remove whole shoots back to the trunk or even portions of the trunk while it is small, but the tree may need assistance selecting a central leader (main trunk), if that is its primary growth form. This may be a case where you consider cutting your losses and replacing this tree with something different that grows at a slower rate and remains smaller overall. 

There are also products that can be applied as a soil drench which will reduce the growth rate for a few years. However, those products are expensive and may be taken up by the roots of nearby plants, with unintended consequences. You could also try root pruning, where you use something like a shovel to cut the roots all around the tree maybe a foot or so out from the trunk. That will stress the tree and could be detrimental during hot, dry weather, but it will reduce the amount of water and nutrients available for growth, thereby slowing the rate of growth. That approach is not without risk, but it might be worth trying prior to replacing the tree entirely. The further out from the tree you prune the roots, the less stressful it will be for the tree.

I've called a couple growers and one says prune it in the Spring and one recommends the Fall.  So now I'm totally confused.

Also, would it be too stressful to cut back into the previous years growth?  I'm trying to maintain the fullness and if I cut this  years growth I'm afraid that it will be rather top heavy.

Also, would it be too stressful to cut back into the previous years growth?  I'm trying to maintain the fullness and if I cut this  years growth I'm afraid that it will be rather top heavy.

Yeah, those photo apps can get you close, but it isn't possible for them to accurately identify every plant! In your case, it is fine to prune now. This particular cultivar will benefit from annual pruning just after the shoots have elongated. Halving each new shoot is one way to do that, though you might need to be a bit creative this first time. Otherwise, it can start to get leggy. Pruning younger shoots encourages new, denser growth at every cut through the development of additional buds near the cut.

It won't hurt the tree to remove older wood. You can safely remove entire branches of older wood back to a branch or trunk, but it may take some time to fill that area back in, because of the low growth rate of this tree. Pruned older wood will not develop buds at the pruning site. Only current season growth will reliably grow new shoots where pruned.

I hope I explained that clearly enough. Please let me know if you need clarification or have further questions.