could be wind damage, also could be aphids or spider mites sucking the juices out of the leaf and weakening it. Whatever it is, if the plants are otherwise healthy I wouldn’t worry about it.
If it’s only occurring on the leaves lower on the plant, it’s most likely just old age. That type of ugliness (and severe bleaching) has been taking place on on every variety I’ve tried growing since the late '80’s. I wouldn’t really worry about it.
That is insect damage and it’s mostly cosmetic so I wouldn’t put much worry in it, the plants will be fine but if it really becomes an issue you can use a general insecticide labeled for edible plants