And weren't the Muslims using cannon in Spain in the 1300's?
Cannon were used by multiple armies prior to 1494. John of Gaunt used twelve guns to batter the walls of Harfleur during his siege of the town during the Hundred Years War. However, they were almost entirely siege guns, fired stone ammunition, and weren't integrated into maneuver forces at all. The Age of Gunpowder/beginning of Modern Warfare is universally agreed on by historians as the Italian Wars.
The Italian Wars, particularly the "Renaissance Blitzkrieg" of Charles VIII through Italy saw the first use of field artillery and widespread deployment of firearm-using infantry. The combination of mobility and artillery firepower inherent in French armies, combined with the infantry innovations of the Swiss, and the use of arquebusiers by the Spanish (and the financing of armies by the new banking families) ended the Age of Chivalry and caused the development of radically new methods of fortifications to replace the curtain walls of medieval castles, which couldn't stand up to cannon and more mobile, larger armies.
Equally, the introduction of the widespread use of machine guns and trench warfare ended the domination of the rifleman.
"Age of Gunpowder" means a specific thing.
