She is actually over 1,000 years old, and is widely known in the Granblue universe as the person who basically invented alchemy. Her original male body was always of ill health and would've died in adolescence; to avoid such a fate, she learned how to use alchemy to create new bodies and transfer herself into them, thereby living indefinitely. This is how she wound up in her current female body, which she views as her "ideal" form.
Her nickname on the internet is "Uncle Cali" (カリおっさん, Cali-ossan).
Note that, because her male form was never even seen in-series, Cagliostro's presence only warrants the genderswap_(mtf) tag if the image references it somehow. See topic #11614 for details.
