Just out of interest was this flight carried out in a sailplane or an aeroplane under the auspices of the UK CAA or EASA?
Just that CAP804 states:
FCL.020 Student pilot
A student pilot shall not fly solo unless authorised to do so and supervised by a flight instructor.
Before his/her first solo flight, a student pilot shall be at least:
in the case of aeroplanes, helicopters and airships: 16 years of age;
in the case of sailplanes and balloons: 14 years of age.