I agree that Jane Austen knew what and who she was writing about and very young girls marrying was quite the norm in the Regency era (did not Mrs Bennet think Jane might have got an off from a gentleman when she was but fifteen? Lydia was married at just turned sixteen in her next work,
Pride and Prejudice ) .
What I sometimes wonder is if our perceptions of her characters are too coloured or influenced by watching modern adaptations? Did Colonel Brandon actually look somewhat like the late Alan Rickman, or Marriane Dashwood vaguely resemble Kate Winslett? Was Darcy anything like Colin Firth? Elizabeth was but tolerable in looks until the intelligence in her dark eyes attracted Darcy's interest rather than her pretty looks. I suspect that we possibly sometimes assume this to be the case when Jane Austen may have had much more plain and ordinary looking characters than Hollywood's finest in mind. Colonel Fitzwilliam was not a handome man, neither I think was Colonel Brandon. How much like a silver screen hero was Mr Knightley? Their main attraction was one of great consequence in middle class life, that of money and financial security. They all owned large properties. "Handsome is as handsome does" is an old mandate. Did it apply in Jane Austen's world?
Wickham would have married the plain and freckled Mary King because of money and regardless of lack of beauty. The George Wickhams' John Willoughbys' Frank Churchills etc were all allowed to be handsome charming fellows but shallow and false in reality. Did Jane Austen stereotype her villains this way purposely? Her father, someone she loved dearly, was a normal working and poorish clergyman with a large family and never described as handsome.
Sense and Sensibilty being her first major novel, what exactly did she have in mind? Since she rarely described her characters other than briefly, it is something of an intruiging question. It must have been so in the minds of film directors also when casting.