Research has shown that while most folk over the age of 45 do think it gets better, about 25% of men, and 15% of women, reported that they were actually dissatisfied with aging and sex. A mix of men and women indicated that they were neither satisfied nor dissatisfied as they aged.
As you get older you may want less sex. Women are twice as likely to lose their sex drive as men, but a variety of reasons may be applicable. But it is not a given that normal, healthy older folk will lose all interest in sex.