I agree with this. I really believe that the posters saying 'we had babies at 43 and 47 and we're in our mid 50s with 2 children under 10 and we're absolutely fine,' are saying this because they are coping, and they're OK. (Many of them.) Because they HAVE to be. They have had the children now, and that's it. They can't go back in time.
But they will be more tired and weary and struggle with the children more, and will be knackered more (than someone a decade or two younger.) 'My 54 year old husband cut a tree down today, after a day at work, and still played with our little boy after dinner' type posts make no odds. We can all have energy spurts.
It's a biological fact though, that in your 50s, you are much less energetic and less healthy than you were even 10 years earlier. And definitely 20 years earlier. You can kid yourselves that you're as fit as a butcher's dog at 55, and 'healthier and fitter than a 30 year old,' and I'm sure you're coping OK, but people 10-20 years younger will be coping better (with small children) for the most part.
This is why I don't get people making it sound like a good thing to put motherhood on hold, and tell posters who still haven't had a child by 33-34, they will be FINE, because they and everyone in their 'social circle' had their first baby at 43, and they know LOADS of women who had their first at 48!
If that's true then good for you, but stop telling women in their mid 30s that they have loads of time. It is a fact that once you hit 35, your fertility starts to decline rapidly. Yes yes yes, I know some posters on Mumsnet don't like to hear this, and even deny it and laugh at it, and some posters are going to jump on me and say 'I had all 3 of mine at the age of 38 and older, and so did every woman in my social circle.'
But it's a fact. Your fertility does start to decline rapidly when you hit 35. Actually 90% of your eggs are gone by 30, and at 35, it's down to 2 to 3%! Have babies a bit older if you want, but stop telling young women that they're fine to leave it and leave it til they're 40-odd. Also, some posters claiming every women they know had their first baby at 41 or do, doesn't alter the fact that the average age for a first time mum in the UK is 31..