Which leaves are affected & how many? That is, are these upper leaves (new growth) or lower (old growth) & is it more or less than 1/3 of the total foliage?

If it is old growth, & not more than 1/3 of the plant, than it may be just age-related. On my tomatoes, I find older leaves tend to die off as new 1s grow in.

It is the lower leaves and about 1/4 - 1/3 of the leaves. The plants seem otherwise healthy. So maybe it is okay?

I've also been wondering about them fruiting. They should be starting to get flowers any time now, but I've not seen any signs. Will they produce fruit indoors under lights?