True, but in between 25 and 30, AFAICT, female fertility remains high and steady, and doesn’t decrease very much in early 30s.
ISTM that the trouble with getting more social support for early childbearing is that our society traditionally and persistently ties childbearing structurally to marriage. And very young adults are often not in the best place for forming stable marital relationships, at least in cultures where adults expect considerable amounts of autonomy, and tolerance for social nonconformity, in their adult lifetimes.
There seem to be some communities, e.g. among Black American single mothers, where some people are supporting a more intentional separation of parenthood and marriage. (And they also have higher birthrates than the US average.)
I think that if we in developed nations really want to increase our birthrates, especially among younger people, we’ve got to (a) put more resources into structural supports for making parenthood a doable project financially, and (b) explore other kinds of societal support that don’t automatically assume parental marriage as a prerequisite. Clearly, traditionalist diatribes along the lines of “we need to return to values that prioritize marriage and family” and “we’ll give married couples a (small) cash bonus for having babies”, etc., are not working.