The type of nail you found is commonly called a square-nail, but its actual type is known as a cut-nail. That's because it was cut (by bladed machine) from a flat sheet of wrought-iron ...unlike Roman and medieval and early-Colonial nails, which were hand-forged. Unfortunately, there is no way to date a cut-nail with much certainty. That kind of nail is still being manufactured today, though they are now used just for "special purposes" rather than common everyday usage. They were still commonly used for construction in the early 20th-century. They fell out of favor for house-construction when machinery was developed which could cheaply manufacture cylindrical-bodied nails from steel, which is superior in hardness to the old wrought-iron nails. By the way, the jaggedness of the break in your nail shows it is made of wrought-iron.
Apparently, the widespread "switch" from square-bodied wrought-iron nails to steel cylindrical ones seems to have occurred in the early 20th-century. My house was built in 1926, and I'll testify that its walls, floors, and "trim" contains hundreds of square-nails (of various sizes). But even more of my 1926 house's nails are cylindrical steel ones. So, I would say that the statistical odds favor your nail having been manufactured sometime before the 1920s. Sorry, but I can't be any more specific than that.