Actually the ages in my previous comment are incorrect, since they were based on the assumption that Sheppard was born in 1830, but I recently discovered that according to the records, actually she was born in 1826! (And have now corrected Wikipedia withal.) So all the ages in my prevous comment have to be adjusted up by 4 years, except for the claim that she started the book when she was 16, which comes from an anonymous letter to The Atlantic written by someone who claimed to be her BFF. But it's now pretty clear that she didn't finish the book while she was a teenager, since later parts were clearly written after Fanny's and Felix's deaths in 1847!