FAR 61.58 details the Pilot in Command proficiency check for multi-crew and/or turbojet aircraft. Basically, the proficiency check must be done in any crew- or turbojet every 12 months, and in the particular type every 24 months. I suppose, single-pilot type rated propellor aircraft, King Air 350, or Metroliner, etc., might not apply. Real-world, insurance requirements will be more stringent, probably demanding a (insurance approved) recurrent training program every year. Note, the type eating never really "expires," it's just that a pilot wouldn't be legally current to be PIC until satisfying the regs. As Samten said, for 121 (airline) or 135 (charter) operators, this is more or less built-in with your 6-month and 12-month checkrides.