223 is not a good deer caliber and little if any margin for error.You can get a good deer rifle and use managed recoil ammo to virtually eliminate the kick if he is sensitive to that.The 308 and 7mm/08 would be great choices.
I fall into the "I don't recommend 22 Centerfires for deer hunting" category. Yah, they will kill them, but there are just too many limitations. Go ahead and get him a legitimate deer hunting round that he can use w/ confidence the rest of his life. I was faced w/ the same decision some years ago when my son started hunting. Bought him a Savage bolt action w/ cheap Simmons scope in 308 Win. I almost got a 7-08, but already had handloading supplies for the 308. Started him off w/ reduced recoil handloads. He's been using full power loads a number of years. He's killed 13 deer w/ the gun, all w/ one shot. The keys are: a gun that fits him (may need to cut off the buttstock some), a GOOD recoil pad, plenty of eye relief on the scope, managed/reduced recoil loads, and, when at the bench, good hearing protection and possibly a sandbag between butt pad and shoulder. As he gets older, you can buy a new stock w/ longer length of pull, if needed.