Florence Symons was 22 years old when they married. He has been connected to a person who would have been 18 years old at that time, and she also died in childhood. Her older sister, also named Florence, who was born in 1878, also died in childhood.
South Australia Marriage Index. (Genealogy SA, https://www.genealogysa.org.au/index.php : accessed 9 October 2022) marriage transcript for William Bushel MITCHELL (Age: 24, Status: S, Father: James MITCHELL) and Florence SYMONS (Age: 22, Status: S, Father: William SYMONS) on 12 February 1900 at Res of William Symons Kadina. Reference: District: Daly, Book/Page: 202/600.
The marriage took place at the residence of William Symons in Kadina.
William's obituary confirms that he married Florence Symons, the daughter of the late Mr and Mrs William Symons of Kadina.
https://trove.nla.gov.au/newspaper/article/92435804
This William Symons didn't live in Kadina.
The Florence Symons below is the wife of William Bushell Mitchell.
South Australia Birth Index. (Genealogy SA, https://www.genealogysa.org.au/index.php : accessed 9 October 2022) birth transcript for SYMONS, Florence (Gender: F, Birth Date: 8 September 1877, Father: William SYMONS, Mother: Mary HARRIS, Place of Birth: Wallaroo Mines) Reference: District: Daly, Book/Page: 191/346.
