Thanks, LBM, we have been listening to ours pretty intently (hard to avoid, really) and have heard some funny sounds, but not too much that sounds like Boc Boc. My hubs swears he heard some garbley Bocs the other day, but I missed it.
My "Middles" are 17 or 18 weeks old, and they each started getting their Big Girl voices between 13 and 15 weeks of age. The RIR succeeded first, then the Welsummers, then the Barred Rock, and finally the bantam Cochin.
I have "Littles" in with the Bigs and Middles, too, and they're 10 weeks old. They still peep. But this time, the bantam Cochin in this group is ALMOST bokking. That's much earlier than the last group!
My little girls started to bok at about 12 weeks. They're about 17 weeks now, and they're full out bok-boking. I love how funny they sound in the beginning. One of my EE's is quite a talker, and she tells me all the latest chicken gossip in her new bok bok voice. LOL!