Writing for OneSTDV's blog, The Undiscovered Jew takes a look at fertility rates by age range and finds that from the age of 30 onward, IQ and white fertility correlate positively at the state level. That is, the smarter the state, the more fecund its 30+ population. The conclusion TUJ arrives at from this is that efforts to extend the span of viable female reproductive capacity using artificial reproductive technologies are the answer to below-replacement white fertility. Aubrey de Grey's drive to retard (and ultimately reverse) the aging process promises to carry eugenic consequences with it.
In the comments, Richard Hoste points to the same concern Francis Galton had 150 years ago; if one group breeds earlier than another group does, even if the total fertility rate of each group is identical, the early-breeding first group will outnumber the late-breeders of the second group.
A simple thought experiment demonstrates this. If hobbit couples have two children at age 20 and elf couples have two children at age 40, their TFRs (2.0) are identical. However, after 80 years, there are ten hobbits but only six elves. At age 20 (year 20), the first generation of hobbits have two kids. Twenty years later (year 40), their second generation offspring have two kids of their own, just as the first generation of elves are finally having their children. So after 40 years, we have two 40 year-old hobbits, two 20 year-old hobbits, and two newborn hobbits, to just two 40 year-old elves and two newborn elves.
But total population share and realizing replacement fertility are two separate (albeit related) issues. TUJ shows that if the fertility of white women in their late thirties doubled and fertility of white women in the early forties increased eightfold, without any other change in the fertility rates of white women under the age of 35, total white fertility would be above replacement. Although the white population would not grow as fast as the Hispanic population, the absolute number of whites would accrete over time. The formidable problem of an inverted age pyramid already facing Russia and Japan, with Western Europe not far behind, would thus be averted.
The desire for well-adjusted, industrious young people to get to work making babies instead of spending their twenties and thirties obtaining academic and then professional success may be hopelessly quixotic. A la Idiocracy, it's not going to happen on a largescale among those of European descent. For those concerned about the sustainability of white populations, extending female reproductive spans and getting the aging clock to tick in a counterclockwise direction are two of the most potentially fruitful strategies available.