Signing at age 4 above.
Phonological + language acquisition
Juli began using HELP pretty often at age 1;2 for the next few months. Then she expressed in different ways.
Because this sign requires both hands to move at the same time, the infant used the same handshape for both hands.
Robbin Battison in the 1970s observed the constraints on the non-dominant hand of two-handed signs in ASL. Symmetry dominance states that if two hands made the same movement or alternating movement, then both hands consist of the same handshape.
It may be challenging for an infant to move both hands with two different handshapes.
Another observation of the movement in the video is that in the early stage of the sign HELP, the movement was upward and downward repeatedly. Then later in the middle stage, the movement was downward but with one sharp, firm movement. After that, videos haven't been found at this time.