This is an interesting old piece of furniture. Because it's not a standard form, a piece like this would be classified as "folk art furniture" made by a hobby cabinetmaker, rather than a factory made production piece.
As for age, looking at the way the cabriole legs are finished, and the molded block panel on the front, and other features of its construction, I would date this piece to mid-20th century, no older than the 1930s.
This type of dual or multifunction, convertible furniture, in this case one that can be changed from a table to a desk is known as "metamorphic furniture" and as such has its own following of collectors.
A convertible desk such as this is also sometimes referred to as a "campaign desk", in other words an item of furniture that is designed to be portable and practical enough to be used in the field during military campaigns.
As for value, if the desk were repaired so that it folded and unfolded as it should, and you were to see it for sale in an antique store, say, it would have a full retail price of $450. This is also the replacement value for insurance purposes.
Expect to get 30% - 40% of this if you were to sell at a good local antique auction.
I do hope this helps!
Please let me know if you'd like me to explain or expand on any of the above, I would be glad to.