I wouldnt like your chances of argueing with the dvla if its more than 6 months, they will still apply it to his license, i dont believe there is a set time limit.
This type of offence isn't the worst he could have gotten in regards to insurance. Its classed as an IN10 and there are many companies that dont add a big load to premiums for this conviction.
If he has provided false details as qapmoc said, they will process the conviction anyway and then more than likely increase the fine and the person may have criminal proceedings brought against them.