Anna Karina, of course, did this so beautifully (proving the fundamental distinction between childlike & childish)-- at once childlike and womanly, intelligent, sophisticated. In this case it's not about "looking young" (or belying your age) but conserving/reinterpreting something of the magical aesthetic essence of childhood-- an "innocence" which is not in conflict with experience or maturity. (Makes me think, in poetry, of William Blake. And the relation to childhood of the Romantics in general.)
This is also why I like Charles Anastase. I think there will always be something, in my style, of the schoolgirl... (which others may see as, say, the "librarian"). Knee-length A-line skirts, cardigans, mary jane shoes, glasses, plaid, peter pan collars, etc...