I doubt 27 year olds nowadays look younger than 27 year olds looked in the WWII age.

You have to keep in mind two things: Today and in the past there are/were a lot of people that look younger or older than the average people in their age. So even if you take 27 year olds from today, or two 27 year olds from the past or one from the past and one from today, they most likely won't look the same age. Secondly, the picture appears to be two "photos" (the WWII one isn't actually a photo) someone slammed a text onto, without any source or proof. Considering the fact where that comparison actually comes from, this picture is more a political statement than a historical one, which already makes it kind of borderline to discuss here.