Boys are such strange yet delightful creatures. Our oldest son, who has just turned six, recently declared that when he grows up he is going to be a policeman but he is not going to be a husband or a father because he never wants to mate!
My husband and I smiled. “Whatever you say, my boy,” knowing full well that he will be completely at the mercy of testosterone at many points of his life, and in about ten years he will probably deny that he ever said that.
Steve Biddulph in his hugely readable and valuable book, Raising Boys, describes the testosterone cycle. As early as 6-8 weeks in utero testosterone starts being made as Y-chromosomes begin developing in the cells. By 15 weeks in utero the testicles are formed and make extra testosterone. At birth, baby boys have as much testosterone as a twelve-year old boy!
By four years of age, these remarkably high levels have tapered off to merely one-fifth of the level at birth. However, between the ages of four and five, these levels once again double and then drop back by half by the age of five. What a rollercoaster of a year – which probably explains a lot about our four-year old. He is a bundle of rough and tough, always toting a sword or a valiant knight ready to take on the next heroic battle for greatness.
I am digressing a bit, but this seems to be exactly what Alex’s teacher described last year as he entered Grade 00 (4 turning 5). She said that when she starts off each year with 19 new boys she thinks, “Oh my goodness, what have I done!” But slowly as each boy turns five she falls hopelessly in love with him and by the end of the year she admitted to crying when they leave.
Anyhow, back to the big T… Between the ages of five and eleven, these levels increase in relatively slow and stable manner and seem to plateau slightly between the eleven and thirteen years. By fourteen years of age though testosterone levels have peaked at almost 800% of the levels exhibited in toddlerhood. The reorganization of the brain caused by this rapid growth results in your boy being dopey and downright disorganized for months. Be gentle with him for he is in the throws of a biological revolution. These levels remain in their twenties but as the body starts to adjust it becomes more manageable and stable. Humans in their twenties are their peak reproductive peak. Worryingly, for boys, the late teens and twenties are most vulnerable to death and serious accidents as a result of the behavioural effects of these high testosterone levels.
Bringing Up Boys ... Raising Good Men 
Thanks so much for this information. A week ago emerged a monster in place of my usually placid four year old son. Now I understand he just needs some understanding and lots of love.
I am so pleased that the info on Testosterone helped you out with your four-year old, theramblingred. We are so often warned about the “terrible two’s” etc but little prepares us for the fours, which I found extra tricky with all their testosterone, and added verbal and physical skills. Wishing you all the best in your parenting journey!