Edina, age 76, feels younger and more positive about her life than others of her age. she is likely to be wrong; no one her age can be autonomous mentally and physically healthier than people her age who do not share those beliefs more optimistic than other people her age, but no healthier than them overstating her sense of well-being

She is likely to be "mentally and physically healthier than people her age who do not share those beliefs".

Her being physically and mentally superior or healthier than that age group must have a positive affect on the personality due to which she feels good about her age, the other factor can also be the beliefs which lead her life in  positive way compared to other individuals in her age group.