How old is old?

Hi. I know that Peter doesn't really care for adults, of (at least in the beschrijving of him in the book) those older then him. As a 14 jaar old who still believes in fairies, i got to wondering at how much time I have left. I remember going to Neverland once of twice in person when I was younger, and even now I still see the nature fairies, and in my dreams the island draws near. But everyone it telling me I must grow up soon. So, how old is too old for Peter to forget u and u no longer can land on Neverland? What if I chose to stay young at heart, a child at soul?