This question cannot be answered satisfactory, as the asker has not specified a country. Independent countries have different rules regarding pornographic images.
However a general take is that all people involved in the imagery, i.e. the photographer, the person or people being photographed, and the person viewing the image, must be older than 18.
- I wouldn't put naked pictures of myself on the internet or anywhere for that matter, even if it's for a loved one or something. Once you show someone, it never goes away.