Around one-in-four sex crimes that were reported in 2019 happened more than 10 years ago.
Two-thirds of detected sexual crimes took place less than a year before they were reported.
Women are the victims in almost 90% of cases reported last year, CSO figures show.
"The reporting of sexual violence crimes by victims, which continued to increase in 2019, encompasses the reporting of incidents which occurred recently (62% within one year), as well as the reporting of historic cases of sexual violence," explained CSO statistician Sam Scriven.
The figures showed the majority of homicide victims (82%) and physical assault victims (59%) last year were male.
The vast majority of offenders are also male, according to the findings.
"In 2018, most suspected offenders in detected homicide, sexual violence, and physical assault and related crimes were male," the CSO's statistician added.
"Just one in 50 suspected offenders in sexual violence crimes in 2018 was female. Eighty-four suspected offenders for detected sexual violence crimes (19%) were aged under 18 when the crime took place."