Parental marriage consent
Until only a few decades ago, spouses under thirty needed parental consent for their marriage.
Normally, the parents were present at the wedding and signed the wedding certificate to express their consent. The wedding certificate may contain phrases like alhier aanwezig en consenterende (here present and consenting), or [zij] hebben ons verklaard in dit huwelijk toe te stemmen ([they] declared to give permission for this marriage).
If one of the parents was dead, this will be stated in the marriage certificate, and only the other parent had to consent. The marriage supplements will contain an extract of the death record of the deceased parent. If both parents were dead, the grandparents had to consent. If they, too, were dead, the marriage supplements should have more information on both the parents' and grandparents' deaths (occasionally the information was also copied into the marriage certificate). In earlier marriage acts, though, you are more likely to find a statement that the grandparents have been dead for a long time, and that nobody knew anymore where and when they died. In this case, the spouse did not need parental consent.
This image is a part of the marriage certificate of Jacobus Frederikus Winter and Johanna Helena Maria Hoogenbosch. It states the mother of the bride was deceased, and the father of the bride was not present. To give his permission, he had to visit a notary who would then create an act of permission. The marriage record states toestemmende bij authentieke akte, consenting by authentic (notarial) act. This act should be included with the marriage supplements.
If the parents of one of the spouses did not consent, it was possible to request the county court to consent on their behalf. This happened to Jacobus Frederikus Winter, in the marriage certificate above. He had to go to the county court, and the court granted consent on behalf of his parents (in theory the court could also refuse consent, but I am not aware of any case where that happened). The marriage record states that consent is obtained by court intervention (the above marriage act contains the statement voor wier toestemmingen de tusschenkomst van den kantonrechter is ingeroepen, for whose consent the intervention of the county court is invoked). The marriage supplements should have an extract of the court decision.