From Janus and Janus (1993)

                  Frequency of sexual activity

                   ANY sexual activity         Masturbation
                     Weekly or more           Monthly or more
 

WOMEN

AGE

  18-26                     68%                       27%

  39-50                     68%                       47%

  65 +                      74%                       27%

MEN

  18-26                      72%                      51%

  39-50                      83%                      54%

   65+                       69%                      50%