It's not really propaganda, I think it popped up mostly because typical finance leaders are seen as being on the older side. As a Patrick Boyle video on the issue had put it, they had barely been in finance long enough to be trusted with the morning coffee run.

"Kid" is meant to be derogatory, highlighting the absurdity of traditional investors trusting openly irresponsible people with such little experience in such a heavily experience and regulation dependent field like finance. They behaved like spoiled children, with all the drugs and sex going around within the company, gaming while talking to investors etc. It doesn't make SBF look better.