They are all the same age, just a major size difference. I have them in pens that are right next to each other so they can socialize through the fence. Infact, one of the rouen ducklings is constantly sitting at the fence "talking" to the three bantam ducklings...and they like "talking" to the rouen, LOL. My only worry is they are really small compared to the two pekin ducklings I have. All of the ducks are the same age-4wks old. My duck house will be finished soon and I really hope to have them all together so they can share the fenced yard and coop.