I've been there: my first job out of university in 1996 was re-writing a COBOL program that was originally written in 1972, and I'd bet it hasn't changed much

I've been there: my first job out of university in 1996 was re-writing a COBOL program that was originally written in 1972, and I'd bet it hasn't changed much since then. 24 four years between re-writes sounds about right on the COBOL timescale.