I work on a C program that's about 30 years old. We've slowly moved, at our own pace, to C99, then added some C++ here and there.
I don't ever want to have a forceful change, where I have to go and edit code which has worked correctly for over 15 years, just to make a compiler happy.
Similarly, developers are not forced to upgrade to python 3 any more than they are forced to upgrade to GCC 4, in that they can keep using their old tools but they're SOL on maintenance if they don't meet the requirements of the new versions.
So, either your team chose really well 30 years ago, is actively working on an horribly insecure application, or has invested some modicum of effort periodically over the last 30 years to maintain support with the compiler (unlike the developers complaining about Python 3's upgrade window).
It's much easier/better when you are forced into dealing with the change. At least people can laugh at how annoyed others get when they cry "but you broke everything!".
It's called progress. Get with the times or get outdated.