That used to be true, not sure if its true in 2018 though.
40+ years ago, most mothers were in their 20s, early 30s.
Now, most are mid 30s and up due to financial reasons, educational aspiration and starting careers.
I wonder if the doctors have re-considered the 'age barrier' of 35?
It used to be said that older mothers were more likely to have genetically damaged children due to 'old' eggs but I don't think it was ever true, more of a 'bad science' thing. Statistically, its not true.
Seeing as its a Royal baby, I suspect there will be 'rules' about the birth.
My friend’s daughter was pregnant at 35 about four years ago. That is where I learned that is an age considered to be at risk. She lives in a community that is a regional medical center so many high,y skilled doctors.