How early should one start?
Opinions vary, but I'd say you can't go wrong reading Pride and Prejudice to a two-week-old baby. That's what I did when I visited my niece, and there were none of those "what is an entail" or "why doesn't Jane just text Bingley when she's in London" sorts of questions. In fact, my reading lulled her into a deep, soothing sleep.
Some believe in starting even earlier. Just ask Cherilynne Perdigon, daughter of the school librarian at my nephew's elementary school. She began reading Austen to her daughter Sybilla in utero. Sybilla is now 14 months old, and mom's still reading her Austen. I imagine by the time she is five, she may be saying things like, "Kinderdance? At an assembly such as this it would be insupportable!"
[My niece enjoying the beneficial effects of having Pride and Prejudice read to her.]