I've read that the Chinese are trying to do this, they state to make humans that are more resistant to disease. How about they eliminate old age? I have a boss that tells me that old age is caused by the ends of your DNA strands eroding. Suppose they can stop that?
This is a little out of date. About 10 years ago there was something of regulatory void around the world on much of this and someone in China did an embryo modification experiment that sent alarm bells ringing worldwide, which rapidly caused the USA and other countries to introduce legislation. China initially did not, and this caused a lot of concern China would permit gene modifications that the West would not. However, China did bring in its own strict limitations which are roughly equivalent, just it did several years later than the West.
I believe it's actually the Middle East where the concern is highest, as there is a lot of money, relatively unscrupulous doctors and weak state oversight.
There are lots of interesting stories about improving ageing. However, this is all about cell replication. I would point out that this might reduce ageing in the periphery, but it's a bit different in the central nervous system, because there's precious little creation of new neurones after birth. So the body might be in great nick for a 100 year old, but the mind will be going through steady age-related cognitive decline and potential dementia without another big leap in medical technology. One way or another, we'll be dead before any of this technology will be of any use to us, much as all those tech arseholes can cry hot, salty tears that they can't have their immortality.
One concern I heard about is the fear that designer kids will create a stigma against not so designed or not as well designed kids. Another is the Brave New World thing. Don't we need people with varying skill sets? Who will do the most unpleasant work? I'd think in a perfect free market with perfect information, you could end up with a genius quite willing to pick up the trash, as long as you pay a market rate of 7 figures a year.
There is definitely a problem that the tech will be first accessible to the wealthy, who may be able to use it to provide their children (more) advantages over the masses. On the other hand, a lot of development is nurture, not genes. It may not necessarily turn out quite the way they expected.