In the modern world the society is not waiting until their thirties to start a family. I think this is a positive development, but, also, it can be considered negatively.
Firstly, for a young body it is easier to endure pregnancy and a birth of a child. Because probability of the birth of a healthy child is significantly higher. By that, for a young woman it is easier to restore her emotional and physical conditions. Secondly, there is physiological closeness between a mother and a child. As, due to a shorter time distance in ages mothers are able to have the same interests in diferent fields of life, in result, it leads to mutual understanding in relationships in future. Thirdly, young couples encounter with the problems in parenting, and in these occasions they can ask their parents to help them in fostering children, and being young and strong enough with great experience to assist the old ones are glad to share thier time with grandchildren.
However, it has a negative effect. Without any experience living with each other on one territory and being in constant contact, young people can not be easily used to each other, which, eventually, leads to quarrels and misunderstanding, based on everyday routines, whereas, being over thirties people are more patient and more adaptive to each other. In addition, young parents do not have responsibility, inasmuch they do not know how to treat with a child, and they don’t have money for ensuring a good life that lead to fatigue and depression, and, it, in its turn, reflects on both partnesr and a kid in with negative consequences.
To sum up, people can choose themself the age to marry.