Katara is around 85 years old in 'The Legend of Korra'. If you remember her from 'Avatar: The Last Airbender', she was just a young girl of 14 years then. 'The Legend of Korra' takes place about 70 years after the end of the first show, so doing some quick math works out to Katara being in her mid-80s.
It’s fascinating to see her character mature from a rebellious and passionate young girl to a wise and supportive elderly woman who serves as a mentor to the new Avatar. Everyone's favourite Waterbender surely aged gracefully!
And despite her age, she still showcases her awesome Waterbending skills and knowledge! The creators did a great job maintaining Katara’s essence while also showing her development as she aged along the timeline of the Avatar universe.