I’ve been using Jawn since I was a child in the early 90s. I remember my grandfather who was born in the 30s using it.

yep -- first time I heard it was on Dj Jazzy Jeff & The Fresh Prince's "I'm All That" circa 1991. "...set my sights on making a record that people thought was a hype jawn." I was living in New England at the time and all the middle school kids [including me] started saying it shortly thereafter.

We generally assumed it was a synonym for "joint" [as described in the linked article] in the sense of "unit of work," e.g. "A Spike Lee Joint"

[p.s. for the record, "Homebase" is an outstanding LP that still sounds great today]

I moved to Philly in 2008. It was around 2010 that my white, suburban friends started using "jawn" and acting like they had always been using it. By the time I left in 2012, I had not heard any other types of people else use it.

As someone who grew up in the area, I mostly recall it being used in the late 90s, then not really that often afterwards.