Hjalmar's confirmation record in the church of 1864 is linked above. Between birth/baptism and confirmation there were no national censuses so what other record could be existent? Perhaps a vaccination if the parish was still recording that event also... did you check the parish records for the possibility of that type of record?
His confirmation record gives an 1864 date of vaccination, so apparently got done just before his confirmation, might have been required by the pastor.
Thank you - I'm finding it difficult to trace Hjalmar before his arrival in Scotland. Also - apart from being documented as 'father' on Hjalmar's birth certificate, I can't find anything about Heinrik Classen/Clausen other than he was from Hamburg.