If I smoked 1 joint to relive my youth, would it affect my lungs at all?

Not likely. One joint will probably not really do long-term damage. The problem is...One joint may lead to another. And maybe, it may lead to smoking cigarettes...And those will affect your lungs. That said, the smoke from one joint does harm the lung, even if in the short term, because smoke is not supposed to enter the lungs...On purpose.