Re: Is this a musketball? If so, what's the possible age?
Not musket, a smaller caliber muzzleloading roundball. Could be rifle, smoothbore or pistol. It appears to be old, but these have been in use since the first colonization and are still in use today. No real way to say how old.
Re: Is this a musketball? If so, what's the possible age?
Looks like it is around .45" a common rifle caliber. I can see a mold seam, possibly from a forged iron scissors type mold. For NH let's say 1790–1870.