It's only one particular class of humans on earth that is waiting longer. The uneducated, the religious and the poor (which are often one and the same group) are actually having babies at an increasing rate, starting at a younger age.
The global effects of "waiting" on overall population are actually very small when measured against the overall metrics of global population. It's a big world out there. The effects on demographics and culture are actually profound though -- but they are opposite to the intent of those who wait: Populations are dumbing down precisely because the educated have decreased their rate of reproduction.
What is good for the individual family, may be fatal for the society.