Since people would presumably not use that extra time to have more children (they aren’t time-limited now), the result would just be a linear increase in population. The important part here is the change from the exponential models of Malthus etc.
They mostly are actually. Barring the occasional exception there is a definite 20-40 or so age band where most females that have children will have them. This is in part because of society and custom and in part for very valid medical reasons, the chances of children having birth defects go up quite fast past the age of 35.