> To accommodate our education and to achieve financial security we delay commitment and childbirth to the edge of biological feasibility. Even when finally successful, after miscarriages and struggles to conceive (and increasingly, after IVF) we find that the exhaustions of raising young children hit us in middle age instead of in our prime. When I was a teenager, I would stay up all night for the hell of it. As a 35 year old, a few hours of missing sleep set me back for the next few days. When the time finally comes to raise children, we deal with the 1AM nursing and night terrors with the body we have left. In two generations of delayed childbearing the toll of time compounds, and leaves us as grandparents physically unable to provide the depth of support that a young family needs.
Most 20-year-olds are still finding out who they are and don't really know what they want--in a partner, in a child, in life in general. There are real, if unfortunate, biological issues with waiting too long, but also healthy societal advantages.
(Me saying this as a 26-year-old doesn't quite feel right, but I still think I'm correct. I certainly don't feel ready for a child yet, and not merely because of economics.)