So long as they have grit, poults can have mealworms at any age. I wait on scratch until after 8 wks because they need higher nutrition that is found in. 28% turkey or 30%game bird starter. Treats should be 10% or less of total feed.
I give all my birds a little treat of mealworms and scratch. I usually wait until poults or other birds are 2- 4 weeks old and have received chick grit prior to giving anything other than starter feed. I usually start with dried mealworms only and then add scratch grains once they’re outside. As others have said, treats should be no more than 10% of their diet