Half birthdays are the latest milestone, sort of, for adults. They are throwing themed picnics, booking DJs and planning vacations that run into the thousands of dollars. For younger adults especially, traditional milestones like weddings are happening later in life. That has left a void in the calendar that made-up milestones are helping to fill, behavioral scientists say.  Host/Reporter: Dalvin Brown  Producer: @Jacob Ohara @Julia Munslow 📷: Ogechukwu Anwaegbu, Amalia Karaman, Cheyanne Carroll, Zuma Press, My Flying Dress Cancun, F. Martin Ramin/WSJ #birthday #halfbirthday #PersonalFinance #wsj #wallstreetjournal #thewallstreetjournal