The actual terminology you should be using is : are these offences 'spent'
The spirit of the Act is to rehabilitate offenders who have not been re-convicted of any serious offences during specific periods known as 'rehabilitation periods' These periods vary, being dependent on the sentence imposed when the person was convicted.
Where a person has been convicted and sentenced for any offence, other than one which has attracted an 'excluded sentence' (Life imprisonment, Youth Custody for a term exceeding 30months,Preventive Detention, Detention during Her Majesty's pleasure for life or for a term exceeding 30months in respect of Juveniles convicted of grave crimes and Custody for Life) and has not subsequently had imposed on him an 'excluded sentence' during the period of rehabiliation, THAT PERSON SHALL BE REGARDED AS A REHABILITATED PERSON AND HIS CONVICTION SHALL BE REGARDED AS SPENT.
'Excluded Sentences' will NEVER be regarded as being spent for the purposes of rehabilitation.
The periods of Rehabilitation applicable to sentences vary according to the type of offence convicted of, but a person who has become a rehabilitated person in respect of a particular conviction shall be treated as though he had never been prosecuted for,or convicted of, or sentenced for the offence/s which were the subject of that conviction ie: as though he had never committed the offence.
It is stressed that these provisions do not apply to criminal proceedings where a person's previous convictions are being disclosed - Spent convictions would be marked as such rather than deliberately left out.
As previously stated, different convictions/sentences attract different rehabilitation periods and you need to be more specific about the offences committed by the juvenile. I suspect that if they were not one of the 'excluded sentences' they could now be treated as 'Spent'
Similarly the one conviction for Drunk Driving in 1967 could also be treated as spent.
However just because the convictions may now be treated as 'spent' does not mean to say that you do not have to disclose them.
Again you need to be more specific as to why and in what context the person concerned is being asked to declare previous convictions ie: some job applications (eg: Police Officer, Person dealing with young children) require that you disclose all previous convictions whether spent or not.
As you rightly say the Act is quite compicated and I would advise you to seek professional advice if you are unsure (Solicitor /Citizens Advice or similar)
The Data Protection Act 1984 may also assist you.