@MissLucyEyelesbarrow
Yes, you tend to get the parents' perspective on MN (not surprisingly) and not the child's. My DPs had 2 DC in their 20s, and 2 in their late 30s/40s. My two younger sibs had lost both parents by the time they (sibs) were 40. Due to my DPs' health issues, neither of them was able to provide my sibs with emotional or practical support as young adults. Of course, you can be unlucky as a parent and become unwell at any age, but the risk of ill-health is much higher in your 70s than your 50s. When I compare my younger sibs' experience with that of my Dsis and me - the older two - I feel the younger ones really missed out.
@Sakura7
I had the same experience as your younger siblings. I'm in my mid to late 30s now and have lost both parents. I had no emotional or practical support from them as a young adult, in fact I had to support them. My dad got dementia when I was in my early 20s, it's tough and very isolating when none of your friends can understand.
Exactly this. 2 brilliant posts! There are too many self-centred people thinking of their own wants and selfish desires, to think about the long-term effects on the child. If parents have a baby at 45+, the chances of the 'older' parent being infirm and needing care before the child hits 30, is FAR greater than them being super healthy and fit, looking after their grandchildren 4 days a week at 80, and needing NO care ever, right up to their death at 103!!! 
There are some ludicrous posts on this thread. That said, this is the parallel world of mumsnet, and I can count on the fingers of one hand, the amount of women I have ever known who have had a baby when they were 45 or older. I am talking about my entire LIFETIME. (I am in my mid 50s now.) It just doesn't happen hardly ever. Not in real life ... Yet if many of the posts on threads like these were to be believed, you'd think 50-60% of women had had a baby when they were past the age of 45.