Bill and Dipper can pick a gender at 13 but only on January 1st.
Gravity falls Oregon
"Hey Billy/ hey Pinetree!" Both preteens said at the same time making them smile stupidly. Bill the blond and Dipper the brunette for some reason both are wearing white.
"Your ready for gender identification day?" Dipper asked jumping on their feet in excitement.
"Am I?" Bill said excited also "What are you picking?" They asked shy all of a sudden at their crush.
"Still haven't decided." Dipper replied shy as well.
"All our life and we still don't know." Bill said shaking their head.
"Well it is a pretty big step after all." Dipper said smiling taking Bill's hand as they waiting in line with the rest of 13 year olds.
"We can be together if we're a different gender." Bill spook up grinning wide which Dipper returns.
"If you want to be with me one of us has to become a boy and the other a girl!" Dipper said taking off their hat showing it had a wishing bone in it "Whoever has the larger bone is a boy and the littler one is a girl." They said which Bill agreed.
"One,two,three!" Both yelled pulling on the bone and Bill got the bigger piece while Dipper got the smaller one so they both hugged.
"Well I'm the woman!" Dipper said side hugging Bill.
"And I'll be the man!" Bill said said kissing Dipper's cheek.