Mike,
Since you were instrumental in supervision of his training, as 'mentor', you were effectively his 'boss' as regards the information the Board require, so I think it is perfectly acceptable for you to give this man the reference he requires. With the proviso that you are confident in the truth of the situation: your reputation is on the line too if he turns out to be a dud. The licencing provisions are there to protect the common-wealth, after all, from unsuitable persons.
Alan
