First off is this a axe or a hatchet? Next question is how old is it? I'm leaning towards 1800s but I'm no expert that's why I came here lol. Best size comparison i could think of was a normal envelope. thats the white thing. Thanks in advance!
That is a hewing hatchet(broad axe). It's age is gonna be difficult to nail down without some markings. I'm gonna guess it dates from the late 19th to min 20th century. I've found a few on my family's farm that began in the mid 19th century(where my avatar pic was taken).
I'm not sure how brittle yours is, but if cleaned up it should look pretty cool.