Ok, this should be simple, I think. I find that if I press my brake pedal twice while stopping, the second time it doesn't go nearly as far down...almost like it needs two pumps to pressure up the lines. I'm not losing brake fluid anywhere, nothing is leaking. Is there maybe some air in the line or is this normal in old vehicles with no power brakes?

Truck's a 61 btw

Thanks for any insight!