Apparently, Americans Like Their Men to Look Like Grown Adults and Their Women to Look Like Teenage Girls

Why is it that,

when a male is young and thin,

in hindsight, we say, "Ha!  Ha!  He looked like a kid!" --

while, at present,

after years of filling out,

he "finally looks like a man,"

while, at the same time,

when a female is young and thin,

in hindsight, we say, "She looked fantastic!" --

while, at present,

after years of filling out,

she "has really let herself go"?