Hello there. Old cast iron is fantastic, but it requires a very specific balance of heat control and fat management to prevent sticking.
When pancakes tear, it usually means the pan was either not preheated evenly or there wasn't enough oil or butter to create a barrier between the batter and the seasoned surface. Make sure your pan is heated thoroughly over medium-low heat before adding a small amount of butter, and let the pancake cook until bubbles form on top before attempting to flip it.