My kids were allowed to handle certain snakes at about 2 years old +/- 6 months. I tell them that they have to sit on the floor and put their hands out. I also tell them not to touch the snakes head and to only touch its back. Now when other kids come by the house my kids will tell them the proper rules.
I always have my hands either on the snake at the same time as the child or very near by. With two unpredictable animals in the scenario who knows what can happen!