The video says one thing I've been saying since I joined the forum. A lot of guys on here try to say that monogamy is unnatural, but I have always maintained that both monogamy and polyamory are natural, as humans are highly adaptable to different situations.
As for young women, obviously they have an advantage when it comes to the number of fertile years they have left. Also, women have childlike facial features which prompt feelings of protection in males. This is even more true in younger females.