Funnily enough my first gigs around the turn of the century were in ASP/JScript! As far as I know that code is still running in production, NT 4.0 or something?
Now I need to track my code down. I think I can find open source code from 14 years ago still in use. Unless the product is defunct or all your code is rewritten, I think it's common that code just keeps running.
I'm sure-ish some of my code from 10 yrs ago is still in production. Though I'm far removed from where it actually runs. Maybe even some of the older code I wrote (which at this point is ~ 15yrs old) might be still around (at a different place)
5 yrs ago? No problem. I even have to still maintain the darn thing.
Of course, different companies, different cases, etc.
I'm in the weird position of code I wrote 15 years ago still being a common thing I use in production on applications I run today. I worked for a monitoring company that still uses the distant ancestor of the code I wrote, so if I am monitoring applications using their library, it's still got a lot of my code in it.
The oldest code I think is still in production I wrote in 2002, so it's old enough to drink. Still powers a web form as far as I am aware. Funny story - it was in ASP/JScript, so I've been doing "full stack JS" for close to 25 years now?!
I'm still in contact with former colleagues from 4 of my 5 former employers over the last ~20 years (no contact from 1 of them that I left in a hurry). That's how I know code I wrote back then, alongside code that was even older, is still in use today.
This is wild! How can you be so sure?