We would say the ideal is to have a happy medium in the sense that people have a certain maturity before engaging in child rearing because of the tremendous burdens it represents and the great responsibility as well to not make a misstep and be neglectful in some way to the offspring—that undercuts the value and the wisdom in becoming a parent to begin with. There is no point if one raises damaged youngsters and develops an estranged relationship because they have failed to be sufficiently nurturing to be rewarded with children who respect them and want them in their lives for the duration.
When people marry quite young, they are often ill-equipped to give sufficiently of themselves. They are still in a state of dependence, in many respects, having not fully formed their full complement of skills and inner strength to weather the difficult times and to be dutiful and apply consistent energy and even self-sacrifice many times when it is needed. Because of the demands of their young rightly taking precedence, many fall down on the job, so to speak, through immaturity and will be neglectful.
It is better to be older than too young, and the only liability with waiting to an older age than average is when people find aging catching up with them when there may still be a need for them to be a quite active caregiver, if there are difficulties their children are undergoing and need more parental supervision, intervention, and assistance directly.
So, we would say it is not a matter of chronology in number of years, it is a question of maturity being the key in deciding when one is ready for parenthood. This does create a difficult conundrum because the maturity to make a wise decision about readiness is not a given, so the wisdom to know when the time is right will be lacking until it is developed and in place. People will have a good sense of this when it has happened but will not have a good sense that it is absent, in all cases at least, so many feel they are ready when this is truly not the case and it is simply their immaturity, and inexperience, and being naive that leads them to move too quickly to become a parent before they truly are ready for the responsibility.