I have two DDs with AS who were diagnosed at 12 and 7 YO.
Until DD1 was 12, she was, in everybody's opinion, a quiet, very compliant, very academically able, studious, pleasant, polite child who seemed to be happier with her head in books or around horses than with her school mates. Her teachers used to say every parents' evening that they wished they had a class full of children like her.
At 12 she started high school and her world came crashing down. All of her masking and coping strategies were inadequate to deal with the much more challenging environment, she missed a whole year of school and mentally she was in a complete mess for months. She eventually went back to school in year 9 with a statement of SEN and a place in an mainstream autism base attached to her high school. It took a very skilled and experienced psychologist to work out that she had AS and even after diagnosis, so-called ASD specialists in the school loudly questioned her diagnosis.
When I read properly around AS and ASD, a lot of things about DD1's needs and behaviours suddenly made much more sense. With her diagnosis, she also became happier because she realised why she had always felt such an outsider.
Up until that time, I thought you could spot a child with ASD a mile off. I was so wrong. The symptoms can be very subtle in their presentation but that doesn't make them any less disabling as the child gets older and it doesn't mean they need less support.
I soon realised DD2 also had AS and asked for her to see an Ed Psych. The Ed Psych actively ridiculed me for bringing the idea up saying she could see no evidence whatsoever. A few months later, DD2 had a diagnosis and a statement followed a year later by a move to a school with a specialist unit.
I wish someone had pointed me in the direction of reading around ASD when DD1 was 4 and hated birthday parties or when she begged not to be taken on holiday, crying every night to go home. It could have saved her an awful lot of distress when she was thrown in the deep end at high school and then punished for not being able to cope.
Please listen carefully to your family. They may be giving you the power to stop your DS going through the hell my children went through. Read and read about AS and ASD. You never know. They could be right and, if they are, knowing now could be such a precious gift for your DS.