The male version of a Cougar.
....The viper makes sense because older men can both act like snakes and they have "trouser snakes". Furthermore, like a viper, a powerful snake, the male version of a cougar has had the experience to know how to use his snake much better than a younger man.
It is important to note that like a Cougar, the Viper has an age range, typically between 45-55, but definitely no older than 60.
Scott Bakula is such a viper, just watching him on TV makes me damp.
Harrison Ford's days as a viper are definitely over.