Will an old well water tank reduce pressure?

Well water pressure is reduced for a number of reasons. Bladder-less water tanks actually lose air pressure over time because the water absorbs it. In this case, pressurized air must be added to the tank to keep the pressure appropriately high. Old tanks are vulnerable to inner corrosion. Eventually, the seals around the air intake valve or inlet and outlet piping could fail, further inhibiting proper air pressure.

Corrosion-Resistant Tanks

Modern well water pressure tanks are often glass lined. Like water heaters, this helps them resist internal corrosion and last longer. Similarly, "captive air" tanks keep water and air separate with a rubber bladder. More than the tank itself, it is likelier that the pump controls, piping seal or bladder itself will fail with this type of tank, leading to a loss of pressure.