What is a primary lung cancer that would cause multiple small lung nodules less than 5 mm when found?

Likely not lung canc: Multiple bilateral small lung nodules in someone of your age would more likely be from prior infections. If from cancer, they are more likely metastases from another cancer (eg, breast). If metastases from a primary lung cancer there would more likely be a dominant lung mass.

Unusual: Consider some cancer superimposed on histoplasmosis. Metastatic, military cancer from melanoma, breast can have unusual appearance. Alveolar cell can be multiple lesions , but not like the description.