From my experience, being "good" at vibe coding is more about being unable to detect flaws in AI generated code rather than being able to code well. Add AI to the workflow of someone who actually understands scalability and maintenance and that won't be able to get past a couple functions before they drop the AI.
Also, assuming this kid gets weekends off, he would be writing 12k lines of code each day. I don't think the average programmer could even review that number of lines in a day, so there's likely no actual supervision for what the kid is feeding into the codebase.
I'd estimate within four months the project will be impenetrable, and they'll scrap the whole thing.