I reckon pre 1970 but have no data to back it up (Score 1)

A lot of banks use mainframe and AS/400s (Now IBM i) technology, one of the precepts of these systems is the ability to code once and carry forward the compiled program without recompiling, desipte underlying hardware changes (e.g. processor upgrades) both systems are capable of using IBM's RPG (Report Program Generator) language which as it's name suggests start around the time of punch cards, so I suspect programs written pre Unix day zero (1st Jan 1970) if you can believe that.