The back is definetly plywood which has been stained. Based on the machine made dovetails, the modern finish, the secondary wood in the drawers, the style and the plywood, this desk would have been produced in the first quarter of the 20th century. Based on the wood, it does look to be a Vermont piece of "rock maple," which was very popular in machine made pieces in the early to mid 20th century. The 1920's would fit the time period perfectly as a production date , as the style is indicative of the era.
In the current market you would be looking at a resale value of 275-400USD for the writing desk in good to excellent condition.
Any damage to the finish, the wood, or the structural integrity would detract from the resale value .
I know it's not the news you probobally wanted in reference to the time period, but I do hope the information was helpful to you today.
Thank you for any positive feedback you can give for my service today,