It's the reverse! They're saying the kid is doing great!
Sure but GGP is saying that if it wasn’t a high schooler, they would criticise the project.
Therefore they would criticise a project based on the author’s age.
Re:Show HN: Lucia – 3kB Vue Alternative
by shermanmccoy on Monday October 26, 2020 @12:54AM
(#24892935)
"killing it" is slang for doing really well.
I don't see why that's relevant. You shouldn't shit on someone else's project regardless of age.