ok so this is about why isfp and entp don't find each other. i have read here from time to time about why we don't connect and how we get side tracked by other people and don't dualize. it's a small tragedy or a larger one depending on how you look at it.
isfp lives in the middle of the crowd surrounded by people and able to get along with them all, loving all, in all ways. entp lives on the fringe of the crowd, preoccupied with Great Thoughts about Infinite Possibilities. entp will follow interesting and abstract leads, coming back, like prometheus, with some new invention to try to sell, caring nary a whit about what people think.
isfp can be said to be able to get along with anyone, even the most difficult. so they get married and even if they pick the wrong socionic type, will be able to manage it easily. they may miss out on their dual, being surrounded by all their friends and associates.
entp has to struggle through relationships and may miss their dual for not being where their dual is...
i do not believe that it is at all likely that a male isfp of middle age will be available. i think they will have been snapped up long ago. and even if they are not with their dual, they will have found a way to make it work, and will not be willing to endure the discomfort of the conflict that comes with divorce. isfp men who are in their 40's and single are sure to be a rarity.
consequently, i believe that the socionic theory of the superiority of duality has limited practical application for entp females in mid life.