Is it only on the bottom leaves or all through the plant? is it in the sun and did you splash water on it when watering? It looks to me like sun scald. I've grown them for years and have never had one that got leaf spot. I could be wrong but I think they are pretty disease resistant.

Looks to me like the effects of edema. This typically occurs as the result of overwatering during cool or humid weather. So it is more of a scarring rather than a disease or insect issue.