But so many people on this thread became grandparents well before 50. and I am not so sure that marriage and parenthood in mid-20s was as predominant as suggested.
Looking at my own family, DH's and DDiL's, late marriage and late grandparenthood is the norm. Our familes have a diverse range of back grounds from Irish immigrants working as day labourers and living in poverty, through car factory workers, office clerks, to, as we reach more recent times, academics, teachers, chartered engineers and other professional people. Yet on average the age for a first child over all generations is around 30 and first grandchild is 60+.