While I was looking for my first one-bedroomer after living in a series of share houses for almost a decade, I went to visit my grandmother.
J: "So Nana, I've decided I'm looking for a place of my own. I'm tired of sharing."
Nana: "Oh yeah? Will you be happier on your own? Won't you get lonely?"
J: "Hmmm, yeah maybe. But it's not as if people won't be around to visit all the time. Besides, I feel like it might be time to, y'know, like, grow up 'n' stuff."
Nana: "Don't you dare! Don't grow up until you absolutely have to! I haven't grown up, I'm 92. You keep clinging to Peter Pan for as long as you can!"
As drdave says, Peter Pan Syndrome is a pop-psychology term that describes someone who shows an atypical affinity for young-ness: who clings to their youth in a way that raises eyebrows or commentary, and who spends time socialising or recreating with people noticeably younger than them.
There is, though, a formal terminology that applies: Puer æternus is Latin for eternal child. It comes from Greek and Latin mythology, wherein a child god stays a child in æternum, displaying a mix of childlike and mature traits.
Jung described the puer æternus as one of the archetypes, a "primordial, structural element of the human psyche". The puer, he says, is the obverse of the senex, which represents discipline, order, and control, and as all archetypes do, the puer has both a positive side and a negative one: newness, growth, hope, wonder, and innocence are just as much a part of Peter Pan as refusing to grow up is.
And that's what my grandmother wants for her family and for herself. Sure, Peter Pan Syndrome can be about being unable to cope with adult responsibilities; it can be about emotional immaturity, it can be about fear of commitment, and in some exceptional and unrepresentative cases, it can violate social norms of behaviour in ways that are frowned upon or even illegal.
But I, for one, quite enjoy using the ticket my grandmother gave me to Neverland. Didn't stop me from getting my own damn place, though. Nothing wrong with growing up kicking and screaming.