There's nothing fundamentally wrong with being young or not having ever held a real job. There are certainly great founders who have done an admirable job despite their youth and lack of work experience (Zuckerberg comes to mind), but they are few and far between. It's just that these sorts of complaints about juvenile behavior are entirely understandable when you consider the founder's profile.
And to be fair to sama, I haven't seen any comments from YC alumni about how he compares himself to a gangster rapper. However, the trend of VCs pontificating on Twitter about topics that they don't have a good grasp on is somewhat irritating. The only person who has truly demonstrated the ability to "go deep" on (multiple) extremely complicated subjects, and successfully put his time/money where his mouth is, is Elon Musk. And even he showed a typical lack of self-awareness in his younger days[0].
0: https://www.youtube.com/watch?v=kSHUha9ABNY
