It is hard to pinpoint exact ages for the characters because the novel does span a time period from 1775 (beginning of Book One) to 1792 (beginning of Book Three). Dickens does, however, give the ages of most of these characters when they are introduced. Lucie Manette is said to be 17 in Book 1, chapter 4, Charles Darnay is 25 in Book 2 chapter 2, and Madame Defarge is 30 in Book 1 chapter 5. We can assume that Sydney Carton is similar in age to Darnay because they are able to switch places at the end without anyone knowing. Dr. Mannette is probably in his 40s or 50s when introduced because he had been imprisoned for 18 years after he was newly married and had a daughter. Also, he is described in Book 2 chapter 2 as not looking too past his prime.