re: Since the average age for first marriage is now 29 for men & 28 for women

Here, I will just give you the important pieces that address your silly "muh, I know 40 year old broads that had healthy babies".

As time goes on, that number becomes fewer and fewer. Eggs may also be of lesser quality as you age
For example, the risk of having a child with Down syndrome is around 1 in 1,480 for women at age 20. At age 40, this risk increases to 1 in 85.