Reduce age-related diseases through deferred breeding

Here is an idea I posted to Halfbakery, the site for discussing half-baked ideas:

Evolutionary biologists have pointed out that one reason for diseases of old age is that, in the evolutionary environment, there was no selection against them. Since people tended to die young from violence, bacterial and viral infections, and starvation, and because people were chosen as mates while young, there was no selective pressure against diseases that strike later in life, such as Alzheimer's disease and, to a large extent, heart disease.

We can fix this problem and permanently improve the human race by applying this observation to test-tube babies. Specifically, an individual needn't decide whether to reproduce his or her genes while young. Instead, they could store their eggs or sperm when they are young. When they are ready to have children, they would use the stored gametes of their now elderly relations or other individuals they admire.

For example, one of my grandparents is still alive, alert, and relatively healthy at age 104. He also has many traits that I admire. If I wanted to become a parent, I would have sperm from my grandfather combined with an egg from a long-lived relative of my husband and implanted in my womb. My child (technically also my aunt or uncle) would be biologically related to me but likelier to be much healthier.

While many high-tech fertility techniques increase the medical needs of later generations (by allowing relatively infertile people to pass on their genes), my proposal would reduce future medical needs. After a few generations, enough bad genes may be weeded out for people to go back to having children the natural way, with the human gene pool permanently improved.