If its an FEV1 expressed as a percentage of FVC you have signifcant lung disease. If the perecentage improves considerably with asthma medications either on the spot with salbutemol or after a month or so of asthma treatment, then you have asthma . Mild stable asthma that has never required medication ortrestment or has never behaved in a significant or unpredictable manner maystill pass certification. Asthma thatdoes not have these stable characteristics will not pass a commercial or PPL without considerable mitigating considerations.
If your pecentage does not respond to asthma treatment you have chronic airways limitation. It would be a matter for the physician todetermine the effect of the aviation environment on lung function, and the requirements of your aviation duties.