I agree with the posters saying it's unfair on the child. Even if the parents are in reasonable health in their 60s and 70s, it's going to be embarrassing for a teenager to have a mother (and father probably!) who is virtually a pensioner. And in many instances, there are going to be all kinds of things they can't do (with small kiddies) because of their advanced years.
As someone said on a similar thread yesterday, people slow down and become more weak and tired, and less active after the age of 50. Why the hell would anyone want a little infant-age child to be running around in their life, and to be constantly there, when they are in their FIFTIES? 
And as someone else said yesterday, who wants to be dealing with TEENAGERS at around the age of 70?!
One of the very few women I know who had a baby in their 40s (at 43 actually,) was constantly pissed off when she started taking the kid to school (when he was 4-5 y.o,) because everyone, I mean everyone including the teachers, other parents, and school nurse etc etc, thought she was the little boy's grandmother. And even at the doctors the nurse said 'awww charlie, your nana's brought you today, how lovely. You gonna feed the ducks later with nanny?'
She was really pissed off ALL the time, and angry, as she could not fathom why all these people thought she was his gran. She was 43 when he was born, and 48-49 in his first 2 years of school. For some reason, she thought (when she had him - when she was 43,) that she looked ten years younger than her age. She also thought at 47-48, that she looked like she was in her 30s.
She was wrong. She didn't look ten years younger than her age at 43, and she certainly didn't look like a woman in her 30s, at 47-48. She looked every bit a woman knocking the door of 50... And people are not going to think that a woman knocking the door of 50, with a 5 year old, is his mother! Most people will think it's his granny.
Some people are under the bizarre illusion that they look MUCH younger than they are, and like this woman I know, find it hard to fathom why people don't think they look 10-12 years younger, and think they all need their eyes testing. 
Anyway, this woman's son is now 15, and he is mortified that his mum looks like a pensioner compared to his mates mums who are pretty much all a generation younger than his mum.
Having a baby past 43/44 is pretty selfish for so many reasons as many people have said. Apart from embarrassment for your kids (with people thinking you're their gran;) in many cases, they will end up as young people who are motherless, (in their late teens to maybe early 30s,) or who are having to care for an elderly and ailing parent at a young age, when they should be enjoying life.
Then when they have babies themselves, their mother is too old and frail to help, or has already shuffled off her mortal coil.
Some people come out with this 'my granny is 99, and as fit as a fiddle and more active than me,' line, and 'my friend's mum who had her at 18, died aged 33, leaving my friend motherless at only 15, so there are no guarantees for anything!' line, as excuses to have babies at an older age. But it's such a poor argument, as there are sooooooooo many reasons to not have babies past 43-44. (I would say not even past 40 actually.)