. Having a child, or two in that matter is a personal choice, so as being married, etc.
That's more of a philosophical argument; To coin a cliché, children are our future, and marriage is a common foundation for a family. Like it or not, many Western, and particularly European countries make provision for the welfare of children, in various ways such as reduced taxation, free schooling (paid by all taxpayers), and family support and incentives - And unemployment of the main earner is deleterious to a child's wellbeing. It is also far more difficult for a family to relocate to find a new job, or if a new job is away from home, it breaks up the family for long periods, and that tends to have negative effects on children.
The advantage given to age is slightly surprising given the ageism rules in the ECHR.