Purity Balls are more popular than ever. That’s the religious ceremony in which a girl (usually about 12) pledges her “purity” to her father and to God until she marries. Balls are like group weddings: dozens of dads wear tuxedos, girls wear (typically white) ball gowns, dads put gold bands on their daughters’ wedding finger, and then the couple has a First Dance together. The average age of first marriage in America is now over 27. That would make the non-sexual Purity Zone (from pledge to marriage) some 15 years long. If we adjust the figure for the demographics of…