let them get to between 16 and 24 weeks old and then Chicken Dinner time!
Of course you can process earlier if they get on your nerves or get mean.
I wouldn't be too quick to wield the hatchet...he can easily take a growth spurt, catch up or even surpass the others. I'm not the only person on here who has seen this happen. I had a little hen a couple years ago that I thought might have been a bantam and I almost gave her away...and I would have, had there been any takers.
Now, she is as big as any of the others and perhaps a bit bigger than some...certainly heavier. JMHO