Really? The latter was immediately useful to lots of people which is motivating, and it had a nice smooth learning curve (html -> js -> php -> databases -> apps -> backend). Learning HTML is the first step to learning how to make full blown apps. Making a browser at 17 is like trying to climb Everest as your first hike. The expected outcome is burnout and demotivating failure. At best you'll learn some C++ or Rust.
17 is an interesting age. There are way too many comments here saying things like, 17 year olds should just do whatever seems interesting or bum around the world or focus on getting into university. But historically most kids were expected to be productive adults at 16 or 18. 17 is about the right time to be thinking seriously about what kind of work you'll do, how you'll make a living. University won't help and will just delay this decision.
Historically people lived very different lives, required different skills, were poorer, had different opportunities etc.
A lot of people will make better decisions with a few yeas more maturity, and spending a few years developing themselves.
University will help a lot of people, and for some it will help.
There is a lot more to life than making a living.
Early web didn’t have JS. Nor PHP. In fact a lot of early web pages were written using static HTML with C++ invoked via CGI/bin for processing form data. So writing a browser would teach you the HTML plus C++ too.
The early Internet (which the GP mentioned) didn’t even have the web. But that’s nitpicking.
17 is a weird age but ymmv. I left home at 16 alone to study abroad. I had tons of free time due to dorm curfews and such. Unfortunately, I was too poor to have a computer and the computers we had access to were completely locked up. (Naturally we waltzed past the locks to play some games but it was also under surveillance)
Paradoxically I coded way more between ages 12-14, I regret my wasted late teens.
Anecdotally, I think it's great advice.
I contributed to a browser engine around that age (KHTML, which later became WebKit and Blink), and while I don't work in browsers right now, much of that knowledge, mindset and of course the professional network have done much to shape my life. And a fairly successful career, for that matter.