Have you checked out this thread: https://www.backyardchickens.com/t/...g-candling-pics-progression-though-incubationWhat do u mean age? I looked up what they should look like at this day in incubation said some veins should be visable!
It's the one I use for comparison. A good share of the time you can, but just don't get too discouraged yet. Are they your own eggs?