What, you really think someone who believes in the value of corrective rape is all that likely to find incest to be disgusting in other cases, such as strictly for their own pleasure? Anyone who thinks rape is okay for any reason tends to combine it with the belief that sex is for their pleasure, the other person should just relax and accept it.
A UK study done on girls in the 1960s, in orphanages, found the average age of menarch to be 11 years 8 months. Remember, a 1960s orphanage in the UK, where nutritional intake could be enough to survive and sort of thrive, but not to the level of the average family in the same area. And nutrition has been linked heavily with the beginning of puberty, with those able to put on a little more weight earlier on also starting puberty earlier.
Logically, this indicates that very likely the average age of menarch for UK girls was probably even earlier. Yes, it is common for girls to start on average around 11 years old, so anyone who’s worried it’s coming down to 12 is probably only experienced with malnourished girls, or has only a hazy connection with reality.
Also, this is average. Almost no one is average. While I can’t quote exact statistics, the age of menarch can easily go a couple years either way and still encompass only about half of girls. Quite a few start later … quite a few start much earlier, and almost everyone knows a girl who was already growing breasts at 9, and if she’d talked about it possibly even having periods.
Another important thing to know, it does not always, or even particularly very often, happen that a girl has her first period, and then everything else develops. Quite a number begin breast growth a year or even two before having her first period.