The emergence of Nicaraguan Sign Language is a very revealing case is this regard: in much the same process as creolization, a sort of "pidgin" of home signs was transformed into a full sign language in a generation by "grammaticalizing" gestures and simple home signs from older children by the younger children. So it doesn't take long for a gesture to move right on Kendon's continuum until its fully "linguistic".
Here is a recent article that covers this in significant depth: https://www.glossa-journal.org/articles/10.5334/gjgl.499/
The emergence of Nicaraguan Sign Language is a very revealing case is this regard: in much the same process as creolization, a sort of "pidgin" of home signs was transformed into a full sign language in a generation by "grammaticalizing" gestures and simple home signs from older children by the younger children. So it doesn't take long for a gesture to move right on Kendon's continuum until its fully "linguistic".
https://en.wikipedia.org/wiki/Nicaraguan_Sign_Language
https://en.wikipedia.org/wiki/Home_sign
https://en.wikipedia.org/wiki/Pidgin
https://en.wikipedia.org/wiki/Creolization
https://en.wikipedia.org/wiki/Gesture#Kendon's_continuum