You just start paying them more when they turn 21. Not sure if it kicks in at the start of the month/day/hour of their birthday though. https://www.gov.uk/nati

You just start paying them more when they turn 21. Not sure if it kicks in at the start of the month/day/hour of their birthday though. https://www.gov.uk/national-minimum-wage-rates https://www.gov.uk/national-minimum-wage-rates You wouldn't lower the pay, you'd likely just start them out at the lower rate.