Any reason why the 6.5 creedmoor wouldn't make for a great youth rifle?

It would make a great one. Has a little more recoil than a .243. I ordered a custom 6.5 Creedmoor from Alamo Precision Riles last week.

I have a Ruger with a muzzle brake and it kicks like a .223

My daughters shoot a 7mm-08 with 120 gr Hornady reduced recoil loads and they love it. Can shoot up to 160gr when they get bigger if needed. Not sure what the upper end of lead you can shoot in a 6.5, but I know with the 7mm-08 you aren't limiting him to just a light gun.

Edit: just went and looked at ballistics. 6.5 and 7mm-08 are damn near the same thing unless your kid is shooting over 400 yards. Both guns are fine.

What is creedmoor?

Get the 7mm.
Your kid can grow into it. It can shoot 168gr bullets.

If you shooting paper at long range get a CM. If its strictly hunting the 7mm is what you want.

As far as whitetail deer hunting in LA, a person would have a hard time telling an appreciable difference on deer from a list of the following calibers: 25-06. 260 Rem, 6.5 Creedmoor, 6.5 Sweede, 270 Win, 7-08, 7X57 Mauser, 280 Remington, 308 Win and 30-06. All but 3 of the aforementioned rounds came from either the 308 or 30-06. Any of the above will do well. Yeah, a short action will be a few ounces lighter, a little bit shorter and (all things being equal) recoil a little less. Where are you going to get your ammo? You're ok if ordering online, but will need to consider ammo availability if buying from a local store. For example, my local WM doesn't stock the 7-08 and it's unlikely you'll find 260 Rem ammo locally. I've never seen CM ammo at my WM. Growing up in the Pacific NW, my first big game rifle was a 270 Win. Nowadays, I hunt w/ single shot bolt action pistols and 2 of my favorite are the 308 Win and the 7-08. When my son started deer hunting at 10 y/o, I bought him a bolt action in 308 Win and handloaded some reduced ammo for him w/ the 125 gr Nosler BT. He killed a bunch of deer w/ it. A few months ago I bought a Thompson/Center bolt action rifle at a great price for a future "grand child's" deer gun. What was the caliber?? 7-08 Rem Certainly there are other calibers that'll kill deer, but you'll be well served choosing from the above suggestions.

A 6.5 CM should be a fine youth gun, but it would be better if there were reduced recoil loads available. Maybe I missed it, but I didn't see any on my search for the CM; 260 Rem reduced recoil is not in stock. The 7-08 and many others have nice reduced recoil ammo. My full load 7-08 handgun shoots 120 gr bullets at 2700 (about what a reduced recoil will do) and it will kill deer just fine.

Good luck and keep us updated.