Many will disagree, but a youth should have respect for the weapon before ever picking it up.
4 is just to young to understand the "finality" of what a gun can do.
Somewhere in the 6-8 range, every child is differant.
Picked up a Rossi 3 barrel set for $199.00 (.22LR, 20 ga field, 20 ga slug), the 8 and 10 year old are shooting the .22 now, they will start the 20 ga this spring.
Slack