um..wow this thread is something.
But I have thought about it when learning about eels.
Eels, apparently put off having offspring until they are about 100 years old and then they spawn like crazy, and then die.
But I guess they don't have to look after their little elvers for too long. They just spurt out eggs, they hatch, and then swim away.
Human babies require so much care, you can't leave them alone for a second. And we only have one at a time, or two or three, at most.
Teen mums - I think often teen mums are naive and have children too young and are then incapable of supporting their child on their own, they really need the support of grandparents and the father.
Hormones - I don't think hormones wane as get older but the fertile window for females to grow a baby in their womb and give birth safely is very small, in your late teens -twenties is probably the best time.
The other thought is, people become sexually active after puberty, and adolescence is a mad learning curve for everyone. It's really crazy. You could have a crush one week and dump them the next. Those under the delusion that feeling is life-long and can only be reserved for ONE person of the opposite sex may have.a rude awakening to find out that in humans, that is not always so.
Adam and Eve were exceptional in the case they were the only two people on the planet at the time...and even then, they stuffed up. So yea