Yes. You can file an amended return and not claim your son as a dependent.
The reason could be that you are correcting the dependency claimed.
Your amended return for the federal and state will take 12 to 16 weeks to process and register the change.
He will have to mail his return for the federal and state and can do that any time if he could be considered independent.
For more information, see:
How do I add or remove a dependent?
Who can I claim as my dependent?
What does "financially support another person" mean?
@ringfence
