* Newly grown hair: This would refer to hair that has just emerged from the follicle. It might be described as:
* New growth
* Baby hairs (though this term is more commonly used for the fine hairs around the hairline)
* Hair on a young person: This would refer to the hair of a child or adolescent. It might be described as:
* Child's hair
* Young hair (though this is less specific)
* Fine hair (because children often have finer hair than adults)
* Unprocessed hair (because children are less likely to dye or chemically treat their hair)
The best term to use will depend on the specific situation you are describing.