What age is appropriate for a kid's chemistry set?

Manufacturers typically label kits 4+, 8+, or 10+. Picks like the National Geographic Junior Chemistry Set and Thames & Kosmos Kids First are designed for ages 4-7 with no hazardous chemicals, while the Chem C1000 starts at 10+ and the Chem C3000 is realistically a teen/supervised-pre-teen kit because it includes a denatured-alcohol burner and reactive reagents.