When does the starte reflex stop being so strong in babies? Is it concerning in a 9 week old? He does it and wakes hisself crying as well as awake.

Normal. I see it strong up to 3 months awake and 4 months asleep. It begins to fade as babies nervous system begins to mature. The kids are often a bit unhappy when these involuntary movements happen, but they are normal.
No worries. This can be present in infants up to 5 months of age. Make sure to check with your pediatrician that all his milestones and other reflexes are normal.