Yeah that's pretty normal for that age. I got a ton of doubles from my pullets last year. Is it every single egg or just a lot of them? I don't think every egg you get being a double would be normal though.
It's possible since they just started laying, all 3 of our 4 green and blue eggs have 2-3 yolks the first 2 wks of laying now they're all settled to normal one yolk. We had leghorns that were laying gargantuan eggs for a while, we thought they're mutants always had 2 yolks. Then they become normal xL size.
No, not mutants! Normal. Means they are pretty healthy and well fed. Just still getting the internal process in order.
Be happy while it lasts, nothing better than frying up a double yoke egg or two for breakfast, or dinner!