First: Everything Joey said.
Second: I mostly finger-pick bare handed - doesn't get much lighter than that - and my Alvarez loves it. Which, of course, underlines Joey's point; have him play them all & buy the one that speaks to him, right then & there!
Third: If he have bucks to invest, many Martins & Gibsons will sound great. Strangely, however, in the lower ranges he will almost certainly do better with a less-revered brand.
Fourth: Of course check out the Ms & Gs - but make sure he try Larav?e, Santa Cruz, Alvarez, Takemine, Breedlove, Yamaha, Eastman, Washburn, and anything else they have hanging around; no telling what his instrument will be until it finds him.
Fifth: Don't make the common mistake of assuming acoustic = dreadnaught. My favorite acoustic body is the Martin M; second is tiny parlor guitars. If he's planning on only playing bluegrass, yeah, a D is the ticket, but otherwise try every body type as well as every brand. And plus 1 to Tony on the all-mahogany; the new Guild GAD M-120 small-bodied all-hog is amazing, especially for under $700 - under $600 without a pickup (of course if you can find an original MIA M-20..........)
Peter
Oops - edited because after I posted, I realized that I forgot the OP; fingerpicking, esp. blues, let me amend my last point to emphasize that a D is his last choice for this; about any other shape will be better - and the M-120 will be perfect (as will a Gibbie L-00, Martin 0, 00, 000, or M, Santa Cruz F or Firefly...) Oh, and don't forget resophonics - they're not just for slide! For his purposes, I'd suggest them in descending order of spider bridge, tri-cone, biscuit bridge; then he'll need decide if he prefers a wood or metal body................
OK, I'll step away from the keyboard; have him go everywhere he can and play everything he can, and don't expect an online buy to matc h an in-store play.
(Message edited by Cozmik_Cowboy on August 18, 2013)