Clearly, older parents do have greater risk of sooner health problems and death. However, I think that some people have a rather skewed view of that risk (which is usual with perceptions of risk - people generally aren't very good in understanding its severity or liklihood)
The chances of an adult dying before they are 65 or having severe health problems (so during a child's childhood perhaps) is present, but low. Therefore, whilst there is an increased risk of these issues for older parents, the risk is still very low. More children will have a parent die who is younger than those with older parents, simply because more children have younger parents. A child experiencing the death of a parent is a terrible thing and it does happen, but it happens to children with parents of all ages.
What is much more likely is that a child who had older parents is more likely to experience the death of a parent or serious health issues and implications during their younger adulthood. Going through the illness of your parents or caring for them or experiencing their death is always difficult. It might be more difficult for younger adults than older ones, but I think the idea that it is impossible to cope with or means it would have been better for those children not to have been born at all is a rather extreme view of things. I guess older parents need to have this issue in mind and make sure their young adult children have enough support around them to cope with this eventuality. Death of a parent is never going to be easy to deal with, but it is a feature of life and dealing with it in your 20s or 30s is not something if horrific proportions - think of the last and other societies where this was very much the norm - not something we'd want everyone to have to face, but something well balanced adults can face and cope with.
Clearly there are people on this thread who have had much older parents and wished they hadn't for a variety of reasons. Some experienced the health issues or death or issues in childhood of having older parents. As they say, their experiences shaped them, but it is also important to recognise these are not the experiences of everyone with older parents. And to say that it would have been better not to have been born than to experience a sick parent in your 20s or whatever is certainly not a typical view, but an extreme one.
And so, all I'm saying is that whilst we do need to recognise individual experiences and to understand increased risks, we also have to hold these in balance when making decisions. The vast majority of children of older parents will have full and happy childhoods and their parents will survive and not have serious health concerns. A number of them will have to deal with parental illness or death in their 20s and 30s and 40s, but most will cope and manage. The vast vast majority will love their parents and be glad they were their parents.