Cold Spring Shops gives an example of the rules for interchange traffic on US railroads
No freight car more than 25 years old may be used for interchange service on the U.S. and Canadian railroads
As far as I know, no equivalent rule exists in Europe, where some quite old equipment is still in use in some places. There are some 1950s Ferry Opens that run though the Channel Tunnel carrying wagon spares, a duty they performed in the days before the tunnel when international traffic went on the Dover to Dunkirk train ferry. There are still an awful lot of 1960s-built HAA 2-axle coal hoppers in service, although EWS are slowly replacing them with modern bogie designs.
There are also a few 1930s(!) SR built “Queen Mary” bogie brake vans in service.
The record for longevity has to be held by four ex GWR “Pollen” wagons, used to carry heavy out-of-gauge loads, and built, I think, in 1906! Probably the fact that they were use so infrequently contributed towards their long life; they weren’t retired until the 1990s, giving them a 90 year working life. All four are now preserved at the Great Western Society at Didcot
