2-3 years max. After that it will need to be unpotted, root pruned and repotted with fresh media. The roots will continue to expand and grow regardless of how well or often the tree may be pruned.

I would ask the nursery salesperson if I could pull it out of the pot to inspect the roots before buying that tree. At that size, it should be in a larger pot and the roots may be hopelessly twisted into a circular mess.

If the roots are circulating in the pot is there a way to fix that? I think I read that the circulating roots can be cut at the bottom or something like that. But that was for small plants if I remember correctly.

Ideally, you would remove the plant from the container, wash off all the existing soil mix and then loosen and redirect what roots you can and remove those that have grown or stiffened to the point where you cannot. Hard to do with a tree of the size you describe and may also be too late to be of much benefit but you can find numerous how to's if you Google "fixing circling roots".