Only successful applications have the pleasure of getting old.

I'm not sure about "any" measure, the average startup probably has no surviving code in production.. Even the average in acquired startups, if we count acquihires..

Success, in this context, means having solved some problem for a meaningful length of time.

That doesn't exclude anything. Code can exist to pad resumes, feed paranoia, and bolster egos, manipulate people, or simply because someone can't admit their own mistakes. Anything can be a solution to a problem.

Yes, those things do happen.

However, that isn't what I meant by the word "problem". I was talking about end-user problems.

All code is legacy, the only code that’s not is the code that’s not written.

So you're saying they speak from experience and know whereof they speak.