It all depends upon the respective socioeconomic and sociocultural factors. Some women are pressured by family and their particular sociocultural group to have children young. Such proponents maintain that the earlier one has children, the better. These proponents assert that once a woman reaches her mid-30s, it is too late to have children.
Then there are women, especially those from highly educated and highly affluent backgrounds who were imbued with the importance of a woman exploring and finding out who she is before settling into marriage/parenthood. These women were further imbued that it is best to have children according to the F.E.P. principle.
That principle is that before one has children, his/her financial, emotional, and psychological preparedness should be in high gear. Many highly educated and highly affluent women don't feel pressured to have children before 35. In fact. many of them are advised AGAINST having children before 35 as the period before 35 is when they are working on and establishing their careers.
Note: Many women who have children before they were ready oftentimes have an underlying resentment towards their children. They feel tied down as they have missed career and educational opportunities. They also feel as if their youth was taken away from them.
Au contraire, women who have had children in their 30s are more contented as they have fulfilled their respective educational and career opportunities. They have also LIVED, so they have NO REGRETS regarding what could have been. They are happier as a result of fulfilling their respective career/educational choices, so they are more contented and fulfilled mothers than the women who had children before they were ready or had them too young.