risk to the offspring for schizophrenia goes up steadily with the age of the father after age 24, independent of the age of the mother

http://www.dana.org/news/cerebrum/detail.aspx?id=1452

, older fathers confer an increased risk of schizophrenia on their offspring. In fact, the risk to the offspring goes up steadily with the age of the father after age 24, independent of the age of the mother. By the time the father is over 45, his risk of having a child who will develop schizophrenia is nine times higher than that of a 20-year-old father. The most likely reason is that men are constantly developing new sperm. Because the precursors to sperm— spermatocytes—divide every 16 days, by the time a man is 55 years old, almost 1,000 cell divisions have taken place. The opportunity for a copying error in the sperm in which a mutation spreads through the generations of sperm by copying itself is, therefore, relatively high.