Adults can use baby shampoo.
Baby shampoo is formulated to prevent tearing of baby's eyes if it were to get into their eyes and formulated for baby's hair to be more gentle on baby's and toddlers.
However baby shampoo can be used by anyone of any age including children, teens and adults.
I commonly use baby shampoo myself as an adult as I find it gentler on my hair and also better just in case I were to get some in my eyes which happens sometimes.
Adults can use many baby care products on their body without any issues.
Adults can also use baby powder, baby lotion and other baby skin care products.
I do sometimes use adult shampoo but I prefer using the baby shampoo instead when I can.
Even my sister uses baby shampoo mostly for washing her hair and prefers it to the adult shampoo.