It's almost impossible to age. A lot depends on soil conditions, weather etc. In the UK I would age something like in this condition as about 50 to 100 years in the ground but that's just guesswork. In dry soil conditions in a sunny climate, it could be older.
yes,very difficult to age.It looks just like the many mid 19 th Cetury axe heads I find.Many of mine were used to break rocks and splitting wedges....yours has as well.Note the smashed end and the mis-shaped eye
Looking at the key hole it looks to be blacksmith forged. Some of those were all iron, while other more expensive ones had a steel wedge that served as the working edge. Its old when ever it was made.