It isn’t ridiculous. If she’ll sleep with a 15 year old, then you have very good reason to worry she might go even younger.
My point is that a line has to be drawn somewhere, otherwise there is no limit to who she may sleep with. Our laws draw the line at 18. Thats not unreasonable.
In some states the age of consent is 17(as is in Florida ?)!
I do not know if any state goes as low as 16.
The age of consent in Mexico is only 13, which gives you an idea how corrupt and perverted that country is.