My Brassy Back OEGBs are 10 weeks, with no visible budding of spurs yet.
The JungleFowl are the same age.
Did your OEGBs get their pointed saddle feathers in super early? My boys have gotten their masculine saddles as early as 5 weeks. Maybe it has to do with testosterone level?
I think leg feathering inhibits spur growth most of the time. It seems to slow spur growth, or cancels it out completely.
I think one or two of the leg feathering genes must, because I've noticed this trend in my birds as well, but my males with more sparse leg feathering, like my Marans and a hatchery Brahma I had, grew spurs at the same rate as their clean-legged broodmates.