I did not order a Model 21 O/U, but I did get an Inverness and an RBL 16 ga both new from CSMC. My experiences with those guns would suggest that, if ordered on Day 1, he should expect about 18 months (approx.) until delivery. If it shows up before that that, celebrate! If a bit later, he can still celebrate a nice gun. If he waited to order, then it might take significantly longer, depending on how many are in front of him, and the configuration of orders. I suspect they produce in "batches", i.e. 2 triggers, straight stock, 28" barrel, get done first. Then another configuration next, etc. Again, this is just supposition on my part, but it seems to make sense.
I also love my Inverness, and shoot it very well. It will be a keeper when I start to thin the herd.