When I worked at a large, decade+ big tech company there were several times I looked at running code that was over a decade old. I was working in a section of t

When I worked at a large, decade+ big tech company there were several times I looked at running code that was over a decade old. I was working in a section of the business that hadn't existed for more than a decade, so that somewhat bounded how old code could be in my domain, but somehow my team ended up responsible for one thing that was much older, and understanding it took some reading. There were other core systems that I also read sometimes that were older, and it was extremely useful to understand their construction and function.