I think it makes a huge difference depending on the professional job.
I had my kids at 21 and 28. I am now almost 40. Although career progression wasn't the reason I had my first at 21. Its actually worked well.
I now run 2 divisions of our company.
I think the difference is, that I studied, qualified and then have been working since, qualifying. I qualified when my oldest was a toddler. I only took 6 months mat leave with the second. I also realise you can't turn back time and do this yourself.
One issue for women is gaps. And when to take those gaps. Usually, qualifying then taking a big gap without plenty of years experience can put women further behind, than if they took a break once they had alot of experience under their belt. So I can see the point posters were making.
But everyone's situation, support, partner, employer is different. So its hard to say what's the best thing.
I am also not a huge advocate for 'wait as late as you can' either. No just because of issues surrounding female fertility.
As I got into my late 30s, I realised i was advancing quickly because alot of women were taking a couple of MAT leaves close together or taking a career break. And also, alot of men were stretched between work and family life. This is just as my kids got more and more independent and I had more time and could be more flexible.
I don't think there is a perfect time. I think you can only do what you think is right at the time and then see how it pans out.