This is such an incredibly personal decision for both parents (or parent in many cases). Often circumstances and fertility issues result in a baby coming along later in life then one would have hoped (such as in my case).
5 years of TTC... 3 years of IVF... one stillborn baby (not due age related issues) yet I still feel young at heart and soul to have kept going.
My age risk ratio for DS was 1:40, my actual risk came back as 1:2,000.
I am not fussed by what society can sometimes say, I know in my heart at 30 I did not feel ready... at 40 I do. I have achieved career goals, have studied, travelled, lived and been educated overseas... had a great ole time and now is baby time.
And at the sametime I congratulate the 20 something year old's too who feel it is the right time to go forth and have babies too.
Power to each woman, how she feels and the support she has, understanding risks occur at any age.