The major blocker seems to be rising credentialism. People could start careers with just high school two generations ago; now at least a four-year degree and of

The major blocker seems to be rising credentialism. People could start careers with just high school two generations ago; now at least a four-year degree and often a post-graduate qualifications seems to be required. Women are fertile from 18 (legally) to about 40, realistically. (After 40 the risk of bad outcomes go up a lot and the chances of conception go down a lot.) If the first decade of that period to age 28 is occupied with getting qualifications, and the next seven years with establishing a career, then only about five years are left. In five years a couple in their thirties could expect to have two children if they are lucky.