Only children below the age of 12 , senior citizens 65 years or older , or full-time Hong Kong students between the ages of 12 and 25 qualify for the concessionary rate . Only children below the age of 12 , senior citizens 65 years or older are eligible for the concessionary rate on all lines . Full-time Hong Kong students between the ages of 12 and 25 qualify for the concessionary rate on all lines except on Airport Express .