I would like to add that your PVP points will always go to the tournament of the
highest age unit in your army in
that battle. So if you attack with only bronze age units, the points go to the bronze age tower. If you add even just one iron age unit into the army you use, the points for that battle go to the iron age tower.
You can even compete in all of the towers by changing your army, attacking some people with bronze age units, others with iron age units and so on