With son #2, we knew right away. He couldn't handle being touched by much of anything, he would scream for hours with no stopping him no matter what I did. As he grew, it only got worse. By 14, he was violent, self harming, and completely out of control. He had been locked up in juvie more than a dozen times by his 14th birthday.
With son #3, there was no clue anything was going on until he hit puberty around 12ish. He was in my alcoholic brother's custody then, and went from being a real sweetheart to sneaking out at night, doing drugs, stealing, and having a very explosive temper. My brother sent him home to me, finally, just over a year ago. He was great when he first came home but after a few months he became worse than ever! Things are finally settled now and we've learned to communicate - but he's still hard to manage sometimes (often!), and I can't talk with him the way I would with his oldest brother.