Diane de Poitiers at 66-years-old looked as youthful as those in their 30's circa 1600. Keep in mind the average life expectancy in the 1600s was 35-years-old and 67% worked outside all day long on a farm.
From the Telegraph UK:
Experts say she was up to 20 years older than the king but her appearance made them look the same age. One courtier said she was "as fresh and lovable" in her final years as when aged 30 and had skin "of great whiteness".
She was unusually athletic for the time, keeping in shape by horse riding, hunting and going on daily swims in the river next to the chateau d'Anet, in northern France where she lived.
Internal gold poisoning killed her; a self inflicted death over time. Amazing what a woman or man can be talked into drinking or taking if it means a youthful appearance or otherwise.