Complex sentence: Bem also drew from six "prospective" studies, longitudinal studies that began with gender-nonconforming boys around age 7 and followed them into adolescence and adulthood; a majority (63%) of the gender nonconforming boys become gay or bisexual as adults.
Split into simpler sentences: Bem also drew from six "prospective" studies--that is longitudinal studies that begin with gender-nonconforming boys at about age 7 and follow them up into adolescence and adulthood. Bem notes that these also show that a majority (63%) of the gender nonconforming boys become gay or bisexual as adults.