Two separate things here.

My lung capacity and respiratory function in general are well above average for my age (as measured very recently) and I have never smoked. However, I never seem to have the breath to play flute or whistle well (nor any other wind instrument) nor is my singing technique that brilliant. I therefore believe that it is a question of breathing technique rather than of lung capacity.

Therefore, John, I suggest you pick up that flute again and get yourself a tutor or teacher who will explain proper breathing technique! (And I should do the same!)

Best regards,

mooman