What is the oldest code in production that you still use?

I started work in 1998, first thing I worked on was part of the Bank of England regulatory reporting software used by 100s of banks. I'm pretty sure some of that will still be in use.

The next thing I worked on was for British Gas for one of their core processes. I changed at least 100 screens and rewrote their daily batch process. I just heard that's still going and unlikely to have changed.

Both systems originated from early 1990s

Our company has COBOL that's from the 80's. There's some Java batch stuff and Oracle SPs that I worked on 7-8 years ago that are still in use.