Cecilia Johanna Gray Ferguson

Cecilia's DN suggests she was 75 when she died in 1936, putting her year of birth c. 1861 matching the confusing details on South African Genealogies Register, stating she was born/baptised on 17.6.1861 or 20.6.1861 in Aliwal North(where we know her father was due to a 1852 application nine years earlier).

Why did the marriage certificate suggest she was 'aged 27'(born c. 1864) when she was marrying a man she believed to already be fifteen years her senior(he was actually twenty two years her senior). If she was born in 1861, this would suggest they both implied they were younger, and their true ages at marriage 30 and 49, rather than 27 and 42. Was it taboo to be 30 and unmarried? Did John want more children, and she wanted to appear to be more fertile?

https://www.familysearch.org/ark:/61903/3:1:3Q9M-C912-8WTQ-C?i=566&...