Certified GKH Gardening Expert
These trees' size will be dictated by the container that they live in. If you want it to remain manageable, keep it in a smaller container. If you are comfortable with it growing larger, then pot it up into a slightly larger container. (This should be about an inch or 2 larger on each side for each repotting.)
They can remain in the same container for years, no matter the size, so when you want to pot it up will be up to you, as long as the roots fill out the container that it is in, now.
Here are some articles that will help: