Also ya·da-ya·da, yad·da-yad·da.
Origin of yada-yada-yada
First recorded in 1990–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Word Origin and History for yadda-yadda
"and so on," 1990s, of echoic origin (cf. yatata "talk idly, chatter," 1940s; and yatter "to talk incessantly or idly," 1825).
Online Etymology Dictionary, © 2010 Douglas Harper