I've been hearing that old sperm and eggs are more likely to produce children with Down's syndrome and other birth defects. Statistically, older women have more children afflicted, presumably that their eggs have aged. I've also heard that older sperm that has been retained longer also carries an increased risk of birth defects than sperm freshly created by the testes.
I do not intend to have children, but if I did, I would want my partner to ejaculate and make me up a fresh batch to create our little one.
I wish I had a source on this to quote, but I came across it quite awhile ago.
I find this kind of thing hopelessly interesting.