According to 「ホンマでっか！？TV」 talkshow, teenage girls are making fun of elder women posing with the peace sign during photo taking. Apparently, you can tell someone’s age range just by the way they do the peace sign in photos.
Teenagers nowadays like to take pictures with the reverse peace sign like this:
Women in their 20s tend to place their hands against their cheeks so as to break the outline of their face, and create the illusion of a slimmer face:
Women in their 30s tend to feel a little hesitant but yet want to do the peace sign, so they do it very reservedly and end up having their hands below their chest area like this:
And women in their 40s and above have no holds barred doing the peace sign: