Age Lift: Everyone is supposed to look like they're forever 25 - and only Amanda Seyfried was that age during filming.
Dawson Casting: An odd example since most important characters even though they look young are often quite old. Cillian Murphy in particular is in his mid 30's playing a character a decade younger (biologically speaking). And Justin Timberlake is in his 30s. Of the entire main cast, only Amanda Seyfried was really 25.