When applying for most jobs the provisions of the Rehabilitation of Offenders Act 1974 apply. Convictions resulting in a community service order become 'spent' after 5 years or (as applies in your case) after 2� years if the offender is under 18 at the date of conviction.
You can (for most employment applications) lawfully answer 'No' to any question asking if you've ever been convicted of a criminal offence.
However some types of employment are exempted from the provisions of the Rehabilitation of Offenders Act. (These are primarily jobs working with, or alongside, children or vulnerable adults. Jobs involving the 'administration of justice' are also included). Applicants for such jobs must declare all convictions, since they're never regarded as spent when applying for those jobs. (The fact that the job is exempted from the Act will clearly be shown on the application form, or in the accompanying information).
At present, whenever an employer carries out a CRB check on a potential employee, all convictions (including spent ones) are shown. This clearly operates against the spirit of the Rehabilitation of Offenders Act, so the CRB is to introduce a 'basic' CRB check, which won't show spent convictions.
http://www.lawontheweb.co.uk/rehabact.htm
Chris