Hi Raisin YankeesinParis,
I just saw your post and while I have never posted online but only ever scrolled through other people's post I really wanted to reply to you.
We are thinking about a 4th child and I am 40 with the youngest being only 7 months. For me the two main considerations are if my husband would be fully on board (can our marriage take another few baby years of total sleep deprivation and no couple time) and second, will we be able to give them all the time they deserve?
For me personally, other considerations are less important, below my thought process.
If you have children at a more advanced age, there surely is a higher risk of pregnancy and birth complications and chromosomal anomalies. But having children in the first place is also a huge risk, because no matter your age things can always go terribly wrong and you will be in constant worry from the day you get pregnant to the day you die. That's parenthood!
Of course, I feel you should think about potentially having a disabled child and the impact on your existing children. But it's not all black and white. I have met many disabled children in my life and the strain on parents and their finances is immense. But disabled children are blessings too and can teach us so much about the small things in life that we do often overlook!
Some considerations here are also thoughts like being the oldest mum in school etc. Well, a friend had a baby in her 20s with a retired older mum, so her mum had loads of time to help, which was fantastic for her. Now, if you'll have a 4th who has children late you would be in your mid 80s and probably not much help. But frankly, I still think it would be better to be born in the first place with an older mum versus to not exist at all.
I am also not a great fan of considerations, such as would everybody have their own room, holidays, etc when thinking about another child. One could use room dividers for a little bit of privacy and with ours, they have decided to all three share a room, although we have 5 bedrooms! As for holidays, they get as much fun from a picknick in the park as a holiday in the sun, all they really need is TIME! And have their basic needs met, of course, such as clothing, food etc but I think you know what I mean.
Everybody is different, of course, and some people will have completely different views but how boring would the world be if we were all the same?
Go for it! :)