Watching some TLC tonight on some home improvement show and this guy says that according to code, compression fittings on a shower p trap can't be used in an area where you can't get to - the example on the show was a second floor bathroom between floor joists. Is this true? Does everything have to be glue joints?

I'm in a 30 yr old house, 2nd floor bathroom - only access from 1st floor would be through the kitchen ceiling.

Yes, it is true. We always glue traps on second floor.