If someone writes a browser in their teens, they will probably learn more about the web than if they were just writing web pages
Browsers from scratch are multi-year projects for multiple people. Even just skinning and minor tweaks to modern browsers is a deep well for one person.
Building a browser in the early web was actually a very achievable goal for exactly the reasons it isn’t now. There was not JS. No CSS. No SVG. In fact very few widely supported image formats (and graphical browsers weren’t around in the earliest days of the web anyway). TLS didn’t exist. HTML only had a subset of methods. And even POST was usually just managed by CGI/BIN calling an external process, often written in C++ or Perl.
It was a simpler time.
That’s like saying someone who fabricates cars doesn’t have the skills to drive them. Perhaps not, but they’re very well placed to pick it up quickly. They’ve also shown they can do something far more challenging, which is actually better than hiring for narrow immediate skills.
In other words: I’d hire that candidate in a heartbeat.
[Blake Ross] worked as an intern at Netscape at the age of 16 ... Ross became disenchanted with the browser he was working on and the direction given to it by America Online, which had recently purchased Netscape. Ross and Hyatt envisioned a smaller, easy-to-use browser that could have mass appeal, and Firefox was born from that idea ... in 2003 all of Mozilla's resources were devoted to the Firefox and Thunderbird projects. Released in November 2004, when Ross was 19, Firefox quickly grabbed market share ... with 100 million downloads in less than a year