Can someone develop asthma in their 40s even if they've never smoked?

Yes: I know a lung specialist who developed asthma in his 40's. It can conceivably happen at any time.

Absolutely: Though chronic obstructive pulmonary disease (COPD) is commonly associated with smoking, asthma is not linked as closely. Many times asthma begins in chiildhood but there is no age limit. Since you're in your 40's you may want to look into the tirggers that may be causing your attacks. Specifically occupational (factory chemicals, noxious fumes,etc) Animal dander allergies (dogs and cats).