How Old Are the Characters in "Bridgerton"? Let's Investigate

In the season two finale, when Anthony criticizes Colin (Luke Newton) for taking funds out of the family account, Benedict defends his younger brother, noting that Colin is old enough — at "one and 20," or 21 years old — to make an investment if he chooses. The "Bridgerton" books have Colin at 23 by this point in the series, but it seems Netflix decided to age him down a bit.