You should have seen the YC hackathon, it was pretty clear they took the youngest applicants. Speaking like that is appealing to high school and college kids rather than using more formal language. He wasn't addressing journalists and CEOs, he was addressing kids. I think "be awesomer" is a fun way to phrase it for that target audience that is less likely to come across as dry or put them to sleep compared to alternatives like don't bury the lede.