I trained my chicks on it when they were about 4 weeks. They learned very quickly. All it take sis one figuring it out and then the others follow.
Do you have a way of calling them? For instance whenever I have a treat for them I always call "Chook, Chook, Chook" So I used that same call and then would touch the metal tip with my finger so it would jiggle and water would come out. That's pretty much all it took. Just getting their attention. I kept my other water available too. First one chick got it. Then another and another. There was still one that seemed to prefer the other waterer but once I saw that all of them could use it I didn't worry about the other waterer as much.
I finally got the system in a couple months ago. My chickens were about 20 weeks old and were extremely curious as I was installing.....tried to "help" me by jumping on my tool box and getting in my way. After getting it up, I just sat on my little work stool and tapped the water nipples, after a few minutes or so, a couple came over to see what was going on. As soon as I left, the same ones checked out the new "thing" in their run and all were drinking from them by the end of the day. I left the old watering container in the run for a couple of days to make sure everyone knew about the nipples. Then removed it. Have had no problems.
One of the best things I have installed and has saved me a lot of work. Love the nipple watering system!!