Mine aren't tough per say when young but definitely crisper, BUT I have noticed that they have more of a "bite" when young. Almost peppery. Weird.

There are not male and female flowers. They are self-pollinating so same flower or another flower from the same plant works. A lot of times they will pollinate just fine with no intervention especially if you have some air blowing on them but it doesn't hurt to give them a little jiggle help out. I use a little battery operated toothbrush that costs like $5 at Walmart. I just touch the stem or flower and it vibrates it. A second or two and done.

Looks like it could be rust. Take a look at this website.

Could be anything from a water issue to a nutrient issues to a pest or disease issue. Pests you should be able to see. Watering on a fixed schedule can result in too much, too little, too shallow, etc. especially with drip systems. Length of run time and size of emitter is what counts with them. Leaf color is quite dark in the photo like maybe fertilizer burn but that could just be the photo. There are common bean diseases like rust, Early Blight, and Alternaria but it really doesn't look like either of those from the photo. You can Google photos of them for comparison. Either way, remove the damaged leaves. It could just be heat stress and/or sun scorch. Are they producing? How old are the plants? Dave