You want to start that process before he turns 18 because if you do not establish Gaurdianship before then and you need medical care they can give you major issues especially if he is capable in any way of making choices.

This varies from state to state I believe and there is a timetable as to how you have to proceed and in what order you do things. There needs to be at the very least a psyche eval most times and the wait for an appointment can be long so you need to do it early. I would contact a family law lawyer in your state.

Hello there!! Ime not exactly an expert and I'm not sure if it's the same across states but I was advised by an advocate and my an attorney to file for guardianship before he turns 18. It will allow you to continue to make decisions on behalf of him due to his diagnosis. I believe doctors or psychologists typically will write something on your behalf. I hope this helps and good luck to you!