Hi Shelley, I posted on exactly the same issue last month: https://www.backyardchickens.com/th...cking-order-not-laying.1428422/#post-23524786
My BO is the same age and I don't believe she has ever laid an egg. She is at the bottom of the pecking order and always eats last, etc. She appears to be healthy but is very skittery. From what I learned, BOs often lay later, but, I agree, it is a concern.
She may be laying elsewhere if she free ranges. It's not uncommon for them to make nests in other places. Most of my buff Orpingtons have started at 5-7 months of age.They free range during the day. They are eating Purina Layena along with oyster shell and table scraps and meal worms for treats.