Not sure if anyone is still on this thread, but i have the same issue with my female quail!
She is 6 weeks old, and i know for a fact she is 6 weeks because i hatched her myself. but she is still the size of a 3 week old quail.
She has full feathers, and is healthy in all aspects apart from being a lot more tired than the other quail. She seems to have trouble breathing when she is around more quail? When she is kept on her own with a heat lamp she perks up and has no issues...i'm really confused lol.
She is currently indoors with me and some of my last batch of quails, who are now 3 weeks and the same size as her haha!
She doesn't seem to do well off the heat so i can't put her in an aviary, and have no choice but to make her an indoor home to live out the rest of her life.
I don't know how long she will live like this? And i don't know how to keep her company if she remains here with me.
How has your tiny quail been doing?