If, as is most likely, the offences were dealt with by way of fines, then the �rehabilitation period� (that is, the period after which they become �spent and need not be declared) for people under 17 when convicted is two and a half years.
There are exceptions to this if the person is applying for jobs in, for example the police or the judiciary. In these circumstances convictions must always be declared no matter how old they are.
The Rehabilitation of Offenders Act 1974 gives all the details.