I started him shooting a BB gun at about 3 or 4. At 5, I got him a Keystone Crickett .22LR. Over that offseason, I started him shooting my old 410. He got a squirrel at 6 with that. We also developed some mild-kicking 308 Win handloads and he started shooting my wife's Savage Youth/Womens rifle. We went deer hunting once last year but got nothing.
This weekend, he shot full strength 270 and 30-06 loads and didn't mind them at all. Tougher than I was at that age