This 2020 study by Mostert-Kerchoffs has some fascinating information:

• Autistic children and adolescents display bradykinesia.
• There was more rigidity of movement in the autistic adolescent group but not in the autistic child group.
• There was a trend towards dyskinesia as age increased (significant in the adolescent/young adult study group).
• The study used the Abnormal Involuntary Movement Scale (AIMS) to observe movement. This scale was developed for assessment of tardive dyskinesia in adults. You can find a PDF of the AIMS here.
• There are neuropsychiatric disorders that have movement disorders as an integral part of their symptoms ex. schizophrenia.