It is more common during the adolescent growth spurt. That is when my son developed scoliosis. My son had always been very slender and there was no evidence of a problem until he went to a routine checkup when he had just turned 11. Nobody in our family had scoliosis as far as we knew, but then nobody else had hypotonia either. Most members of our family were athletic, which made it more difficult to fit in even in his own extended family.
http://www.scoliosisnutty.com/adam-test.phpWe were told that there was a good chance he could avoid surgery if he wore the brace the required number of hours. This was after months of the doctor saying lets wait and watch to see if it gets worse. It did. If I could go back in time I would insist on earlier bracing and I would fight my insurance company (government insurance) to pay for a doctor more experienced in pediatric orthopedics. The doctor we were sent to was the only one who would accept the low rate our insurance would pay. It wasn't until it was almost too late that we were allowed to see a pediatric orthopedic surgeon who told us there was still a chance that a different brace would work but it is a more difficult brace to wear. My son had been told by the first scoliosis doctor about how his spine would have to be fused to a metal rod if he did not follow the treatment plan, so my son did exactly as he was told. Even though he was sensitive to clothing tags when he was younger he managed to live in a very uncomfortable brace and give up doing things that other kids get to do for three years and it absolutely makes learning more difficult. It is harder for him to concentrate when he is uncomfortable and can't get enough sleep.
Early treatment with the right brace is so important. It is extremely difficult to see a child go through treatment with the wrong brace and then experience setbacks after doing what he was told to do. Our anxiety level is so high right now.