This study aims to estimate six different sexual debut ages in heterosexual Norwegians in six birth cohorts of the general population in Norway. The results are based on a 2020 national web panel survey of 18–89-year-olds in Norway (n = 4160). There was a general decline in the median debut age from those aged 70+ to those 18–29 (born 1991–2002). Oral sex with a female partner has become increasingly common among men at an earlier age across generations. The same pattern was found in women as well with regard to oral sex with a male partner and receptive anal sex. There was a slight increase in median debut age in 18–29-year-olds for receptive vaginal sex (born 1991–2002). The median debut age for vaginal sex was fairly stable for generations of men and women born after 1950.