When you attempt to print a family group sheet for an individual, without a spouse or children, you will receive a message that you must select a family first. If you create a "dummy" spouse, using a given and surname of '_' (underscore) with no marriage it will allow you to select this "family" to create a family group sheet. Once you have created the family group sheet you can delete the "dummy" spouse if desired.

Blank family group sheets are also available under Reports>Lists>Reports>Blank Reports.