There are very strict rules for adopting children in Germany. For details see:
http://www.familien-wegweiser.de/wegweiser/stichwortverzeichnis,did=101188.html
To adopt a child, you must be at least 25 years old and fully contractually capable (“voll geschäftsfähig”). Your husband or wife has to be at least 21 years old. There is no maximum age for an adoption, but it should be in a natural difference to the age of the child in question. A married couple can adopt a child only together. This applies to couples of the same sex as well. It is also possible to adopt the child of a partner, if it is his or her bodily child. It is possible for a single person to adopt a child as well.
As a rule, both bodily parents of the child have to give their consent to an adoption. This consent cannot be given until the child is at least eight weeks old. Under certain circumstances, the bodily father can give his consent before the child is born. In special cases, the consent of the father can be substituted by a legal act of the court, for example if the father cannot be found.
In addition, the consent of the child is necessary. If the child is under 14 years old, this consent is given by the legal representative of the child.
There is always an “Adoptionspflegezeit” (a period of time when the child is already taken care by the person / the persons who want to adopt him or her) before an adoption can be made. During this time, it will be examined, whether the child and the new parents have established an adequate relationship.