This looks to me to be a brown bess bayonet, which were issued in Sweden as m/1808 and m/1812. The dimensions certainly fit, and the markings would suggest that this one was issued to the southern battalion of the Gotland Militia (Gotlands Nationalbeväring), as indicated in your third picture - 7) S 2584, where 'S' indicates the battalion. Other examples may belong to 'M', middle, 'V', Visby, and 'N', Northern battalions. Sweden purchased 23000 muskets of models 1762, 1794 and 1809 between 1808 and 1812 from Britain, so this bayonet may well be of British manufacture, stamped in Sweden with the unit markings. I don't have a source which could reasonably estimate its age, but based on your measurements it could be a 1780 Short Land Pattern or a 1796-1819 BO India Pattern, so the highest estimate would place it at around 240 years old, though it must be understood that this is far from definitive and at best speculative.