It says “First Train” on the front of the train, so you might think this is a pic of the first journey on the opening day of the MTR - 1st October 1979. But perhaps not. Please see main article at https://gwulo.com/node/62741 for further information.
This slide image must have been taken on or after 1 October 1979, but I can’t be more specific than that.
Date picture taken
1980s