Anyone can get married provided that they are not prevented from doing so by a legal impediment.
A minor lacking full legal capacity cannot get married. There are exceptional circumstances where the court may allow a minor who does not have full legal capacity but has reached the age of 16 to get married, provided that there are compelling reasons for them to do so (e.g. because one of the couple is pregnant).
An adult cannot get married if their legal capacity has been restricted in this area by a court. However, restricted legal capacity does not automatically mean that it is impossible to get married.
Anyone who has previously married or entered into a registered partnership or similar union abroad cannot get married unless that previous marriage, registered partnership or similar union abroad has ended.
Marriage between relatives in the ascending and descending order (i.e. grandparents, parents, children, grandchildren, etc.) and between siblings is not permitted. This also extends to relatives by adoption. Nor is marriage permitted between a guardian and their ward, between a child and the person in whose custody they have been placed, or between a foster parent and their foster child.