Throughout various periods of history, the life expectancy of individuals, especially males, was shorter than modern days. Similarly, individuals tended to mature faster, go to combat earlier and breed sooner.
Norse culture has always been based on the natural order of things. A prepubescent child - not being sexually functional - is therefore not meant to have sex under the laws of nature, including evolutionary biology. Furthermore, a prepubescent individual, due to many factors relating to maturity, including lack of hormones as he or she has not gone through puberty yet, does not have a brain that has the capabilities to form informed decisions, and thus consent to sex.
In addition, in Norse culture, a male was primarily valued for his warriors capabilities, and thus core male evolutionary traits and characteristics, and a female for her breeding abilities. Both of which are innately dependent on sexual maturity.
In this context, and as demonstrated by ancient Old Norse texts, sex with prepubescent children in Norse culture was absolutely abhorrent, and sex was in fact conditional on sexual maturity, as in an individual having gone through the process of puberty, making his or her body sexually and biologically functional.
