Can you give your baby probiotic packets under 1 year old ??

I made a post recently about my daughters stool being hard, and like rocks, (I also included her age) many people recommended using probiotic packets in her milk once every day or every other day, shes 3 months old but all the ones I found that were packets said only for 1 year + ...is it one of those times that the age doesn’t really matter or could she be harmed from it ??? A lot of people told me they use them on babies the same age as mine or around her age