Hi, punishment for driving under the influence of drugs is stated under s 57A in the Land Transport Act 1998:

If a person is convicted of a first or second offence against subsection (1) which is (Driving while impaired and with blood that contains evidence of use of [qualifying drug]
,—
(a) the maximum penalty is imprisonment for a term not exceeding 3 months or a fine not exceeding $4,500; and
(b) the Court must order the person to be disqualified from holding or obtaining a driver licence for 6 months or more.

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If the person received 'police diversion' the offence should not be recorded. You could get the young person to be police vetted which would show their record of convictions. If their record shows the offence you can write and ask for it to be amended. YouthLaw can help you with doing this.
Some jobs are going to do a criminal check so it is good to know what is on your record and whether it is going to be clean or not and in this case it should be clean. We like to tell young people to be honest etc but sometimes it is better not to disclose everything about yourself, particularly to an employer. Not all employers are sympathetic or supportive and disclosing personal information can be quite embarrassing, having to do this continually may encourage the young person not to apply for jobs to save face. Personally if you don't have to - don't, you can always judge later whether you want to tell all once you've sussed out the place and people

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