Generally used sarcastically to exaggerate the appeal of a date. The date may or may not be real, and although the date might actually be "hot", as in exciting, it's just as likely to not exist at all or be boring.
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.