Parental age is increasing in most developed countries. Germany has been no exemption in delaying parenthood. The mean age at childbirth has surpassed age 30 for mothers and fathers. The effects of increasing parental age on childrens' cognitive outcomes are controversially discussed. Previous studies associated advanced ages at childbirth with negative health effects while others found that the age related improvements in socioeconomic factors of parents mediate this effect. We test this association on more than 4000 pairs of mono- or dizygotic German twins (TwinLife). The twin study approach allows us to estimate the importance of the familial socioeconomic environment while controlling for the genetic effects of delayed parenthood.