To answer you, I'm 24, and an accountant by profession. From what I've seen, most banks still run some core functionality of their systems in IBM Mainframe, which includes JCL, COBOL and maybe other languages.
Because of space constraints then, file names were limited to 8 characters (someone correct me) and lines of code has fixed lengths. That already made commenting a nightmare. I have 'reverse engineered' scripts that were written more than a decade before I was born. Most have outdated documentation, filenames are a mess to figure out, and over time there have been automated conversion tools that were used to update language versions.
As I said, most of these systems still run some core functionality of the bank, and the people who wrote them ain't there no more, so banks have to shell out lots of money to either fix and maintain these, or to figure out what's happening so they can move to newer systems.
A form of anecdote could be that because IBM still make some form of x64 flavour Mainframe OS indicates that large corporates still have code that's potentially double my age.
