How do you know how healthy your lungs are?any simple way to know?

Pulmonary function: If you have no functional limitation, can do whatever you want w/o feeling excessively out of breath, and if you don't smoke and aren't exposed to environmental risks like chemicals & dust, then really no need to worry about lung function. However, if that's not enough to allay your fears, ask your family doc for non-invasive pulmonary function test to look for obstructive or restrictive disease.