To state the obvious, 2008 was 15 years ago. So someone who was a senior in high school at 18 in 2008, is over 30 today.
So it is true that there's a generation that includes everyone in their 20s and those in their early 30s that have never experienced a significant market crash.
The vast majority of middle schoolers were not trading stocks in 2008.
To have experienced one downturn, a trader must've been trading back in 2007/early 2008. It is safe to say most traders in their 20s today were not active traders back in 2007. I'm sure exceptions exist.
Jobs never really came back.