As ENTP’s get older what does developing Fe look like? I found what INFJ-zen said about interest in family history being a sign of developing Si, really interesting, so I was curious about Fe.

Hm.. I kind of wonder if Fe has as much to do with family history seeking as the Si.  True, Si looks to the past and knowing your ancestry anchors and might provide an interesting explanation for some family/social behaviours that echo down to you, but Fe is about human connection.  

In any case, Fe, being your third function, probably starts kicking in around your twenties, so if you find yourself reaching out more at that point in your life, maybe your Fe is prompting this.