Can I grow an Oak Live Tree in a large container to keep it around 20 ft high?

We live in Whittier California. We have an oak tree in a container that is 18 years old. Have had to get much larger containers through the years. The current container weighs about 500 pounds. The oak tree is currently about 12 feet high and 10 ft wide. It is possible to do what you want to do.

I'm afraid not, not even in the medium term. The tree is unlikely to reach the size you mention contained in a pot because of root restriction; whilst it may remain healthy for a year or three if grown from seed or a small sapling, it will not do well contained in such a manner. This is one of those trees that produces a large and deep tap root, as well as large lateral roots, and growth of the taproot won't be possible in a container; this will compromise the tree's growth early in its life. If you bury the container, the only way the tree will grow on well is if it manages to punch through the bottom of the container and access the soil around and about. It is likely to do that, and when it does, it might as well be growing directly in the ground, in terms of height and spread as it grows. Burying the container confers no advantage in terms of restricting its growth otherwise.