autism

hey ladies my stepson is 12 almost and 3 people pointed out from a very young age he could be autistic what are some signs that u know of for sure .. the signs I think people are pointing out to him having it are °jumping and flapping hands (Dr said sterotyopic movement disorder)

°rolling tongue sound when excited

° he doesn't comprehend simple things

° VERY behind in school hes in 6th on a 2nd and 3rs grade level