When we had our two DCs my DH was 43 and 46 years old respectively.
For us, for various reasons, having children later in life was unavoidable - we met fairly 'late' and we had very unstable housing and employment for the first few years. So I wouldn't have changed it - because the only alternative would have been not to have our children.
However, as time goes on we become more and more acutely aware of how much age does make a difference.
My DH has had far less energy to play actively with our children than he had with his nieces and nephews in their younger years a decade earlier. He is slowing up, as our children are moving towards their teenage years.
Financially it's not ideal, to be mid 50's and thinking more urgently about planning to have enough retirement provision in the future - and still with youngish children to fund through teenage years and potentially Uni.
And the chances of ill health at some point in the next decade do feel much higher than in the past. My DH's Dad died suddenly at 57 of a sudden-onset condition. My DH is now 56, he is acutely aware of the greater possibility that things might go wrong in the next few years - and what that would mean for our children.
Not to mention, having children late has a huge effect on from a family relationships perspective. Many of our elderly relatives have died in the last few years, it has meant children never meeting their grandparents or their grandparents being too elderly and struggling with dementia to have a relationship with them.
So whilst it's true that clearly a man doesn't have a biological clock running down in the same way as a woman (although sperm quality does decline with age) yes, actually, I do think a man of 43 is also approaching being too old - it can certainly be done, but I think it's far from ideal.
And to go back to the main question - whether a woman of 43 is too old.... Reluctantly (speaking as someone who got pregnant with her last DC at 39 and gave birth at 40) I would have to say I think it's right on the cusp. Honestly, based on my own experience (with miscarriage, pregnancy ill health, birth issues) as well as all the points I mention above re. tiredness, finances, family relationships etc I really wish I'd been able to do it a few years earlier. 43 might be possible and it might be right for you, but it will be harder at that age.