A puppy can eat peanut butter as long as the puppy is at least 4 to 8 weeks old and is eating solid foods.
If the puppy is still breastfeeding off it's mother then the puppy is too young to eat peanut butter and could choke on the peanut butter.
But once the puppy is eating solid food then you can safely feed the puppy peanut butter as long as the peanut butter does not contain xylitol.
Jiffy Peanut Butter and most peanut butters you buy at Walmart do not contain the ingredient xylitol and as long as the peanut butter is free of xylitol then it's safe for dogs and puppies to eat.
The peanut butter is good for dogs too because the nutrients and protein that peanut butter contains.