No, I'm not insinuating anything.

The authors charted human brain and divided it into "eras" where they saw significant changes based on age. Major life events can affect brain structure, and becoming a parent is one of the most important adult life events. Becoming a parent in early 30s is common. Just these facts combined mean that being in early 30s correlates with brain changes somehow. The authors explicitly mention that they know about this, and that they didn't control for this it yet.

Back to your question, I never said anything about maturing. It is a well-known fact, that female brain changes after childbirth. There is also research that suggests that first-time fathers brain changes too. This doesn't necessarily mean becoming more mature.

>Becoming a parent in early 30s is common.

Retiring in late 60s. If you make it, becoming too infirm in body to get around in 80s.

These seem like brain changes at these transitions are more likely to be effects rather than causes.