Oh! Bless him, he looks lovely, a fluffy version of ours.
If you inherited him two years ago, he could be any age but sounds like he had some sort of respiratory problem. Perhaps he was too old to fight it off, regardless of the treatments you'd given him. Also we had a cockerel who went blind in one eye. He used to do odd things like stretching his head to one side to see properly so perhaps his eye sight was going too. Could be another sign of his advanced age. At least you didn't let him suffer.