A woman with the kind of refined beauty and attractiveness that requires poise, dignity, and strength of mind and character, things that often come with age; not merely sex-appeal. Usually applied to a woman who is also very well-groomed and from an upper class background.
This phrase is very dated and rarely used in today's English. Those who don't understand the term could almost be insulted by the word "handsome" being applied to a woman, mistakenly thinking you're saying she is masculine.
"Though she had lost long ago her virginal loveliness, she had ripened into a handsome and fruitful looking woman." - Ellen Glasgow
"What a handsome woman she has become; she carries herself so well".