If you're deciding whether you should wait to have children you might think about this: A new study finds the biological clock starts ticking earlier than previously thought. The research indicates that, on average, female fertility begins a significant slide at age 27. Until now, scientists believed female fertility started to drop in the early 30's, with a big plunge after 35. The study also indicates men have baby-making issues. It says male fertility starts dwindling after the age of 35. That contradicts conventional wisdom, which had put the fertility problem primarily with women.