Working on other people's code has a much higher overhead. Before you can make any change, you have to understand how it interacts with the rest of it. It's not unrealistic to spend days studying it, then minutes changing it. Then you move on to yet another unfamiliar codebase - and by the time you get back to the first, months have passed, you've forgotten all about it, and other people have been changing it too so you need to relearn it.
This is why when I interview people who say they've been programming since they were 10, I don't really care - because the experience of working on your own code is radically different from working on an existing codebase.
Yeah, fixing other people's code takes longer, most of the time. I did frequently have to fix bugs in other people's game code, though I've done games long enough that usually I would know how to dig and find the issue pretty quickly.
It didn't typically take more than a day or two to find such bugs, even if the original developer (working on their own code) had tried to find it for weeks and had given up. I could always come in with fresh eyes, and I know most of the ways that people write games, good and bad. In one case I had their "intractable" bug fixed in less than a half hour, having never seen their code before.
So I think I'd probably still pass that interview question, though I'm not looking for a job right now. ;)
That's overly harsh. Having long-time programming experience does help, also in understanding other people's code faster. It's almost impossible to be programming since your 10th and never been confronted with other people's code in one way or another. Either through open source collaboration, reverse engineering, or even studying/improving example code.
(also it means that they are pretty fanatical programmers thus that they're self-motivated)
This is why when I interview people who say they've been programming since they were 10, I don't really care - because the experience of working on your own code is radically different from working on an existing codebase.