Code doesn’t expire. But the programmers do (they die/retire).
If you want someone to maintain that code, old code only gets more expensive. Sure, if it ain’t broke you don’t need to maintain it to fix it, but you need to maintain it to upgrade it. When you eventually need to make an upgrade, it’s going to be expensive. I don’t know if it’s more expensive than making the code not-old though.
Code doesn’t expire. But the programmers do (they die/retire).
The old programmers should document their work and do a proper handoff to a new maintainer. At my work place, other people have to maintain my code, so I write wikis about how it works and do internal tech talks to explain things.