To some degree, this makes sense. Male sperm cells are constantly produced and renewed, so any particular cell that resulted in conception has lived a very short time. Female egg cells, on the other hand, are already in place when the child is born, and from then on, they pick up everything that the woman has been exposed to in her childhood, puberty, and beyond, up to conception: radiation, chemicals, poisons, etc., etc., especially in modern life. So the longer a woman waits to have a child, the bigger the possibility that something will go wrong with the DNA in her egg cells.