Ages in Tolkien aren't really something that lines up with technological progress in the way we consider things like the Bronze Age and the Iron Age, and that concept of technological ages is kinda BS anyway. In Tolkien's legendarium, Ages are considered started and ended by major events as decided primarily by the Elves of Middle Earth - the removal of Morgoth from the world, the fall of Numenor, the defeat of Sauron, and, much later, the birth of Christ.
Ages in Tolkien aren't really something that lines up with technological progress in the way we consider things like the Bronze Age and the Iron Age, and that concept of technological ages is kinda BS anyway. In Tolkien's legendarium, Ages are considered started and ended by major events as decided primarily by the Elves of Middle Earth - the removal of Morgoth from the world, the fall of Numenor, the defeat of Sauron, and, much later, the birth of Christ.
okay but that still doesn't explain why the Third Age had medieval technology and then somehow in the future they had reverted to Iron Age tech.