Their proprietary securities database (called "SecDB" which actually is the internal name for all the quant analytics. The database itself is actually called a "SecServ") and it's associated programming language (called "Slang") are certainly very strange in many ways, but they do not predate the creation of C. In fact it was all written in C++ and Java and then more recently I think they added a bunch of Scala code.

Source: Was a "strat" (quant developer in the front office at Goldman) for 8 years, including starting in the group that used to run version repo, CI/CD pipeline and internal build and distribution tooling for all of this. Think a code pipeline that builds circa 30m lines of C++, 20-ishm lines of Java code daily on 3 different platforms (Linux, Solaris and Windows) and distributes it globally across thousands of machines every 2 weeks and if mistakes are made it can cost millions of USD. And this predates most of what people think of as "devops" by some years (I was there 2002-2010 ish).