A study involving 73 people between the age of 50 and 83 has shown that people who engage in more regular sexual activity scored higher on tests that measured their verbal fluency and their ability to visually perceive objects and the spaces between them.
Participants who engaged in weekly sexual activity sorted the most highly, with the verbal fluency tests showing the strongest effects.
https://www.sciencedaily.com/releases/2017/06/170622083020.htm
Based on a BMJ study of over 5,000 men and 6,700 women, women are more than twice as likely to lack interest in sex when living with a partner.
http://www.bbc.co.uk/news/health-41230891
A study of over 7,000 sexually active women aged 16-74 in the British Journal of Obstestrics and Gynaecology suggests that dyspareunia (painful intercouse) is common and affects women of all ages.
This is something that can be helped with proper treatment and i would recommend seeking advice on this either from your doctor or a sex therapist, however embarrassing it might feel.
Painful sex is often linked to other sexual problems such as vaginal dryness, feeling anxious during sex and lack of enjoyment of sex.
http://www.bbc.co.uk/news/health-38729240
Scientists at Yale University have released an article based on research http://news.yale.edu/
A good introduction for those thinking about having sex therapy http://www.nhs.uk
Wonderful article as a starter for couples http://www.cosrt.org.uk