Summary: yes, this is helpful
This might be smarter than calling attornies who specialize in guardianship who typically will not help the target of the guardianship. (Aka, I'm supporting your suggestion.)
jumping off from this idea, for OP:
A guardianship is more likely to be approved if you are not able to manage your financial, legal or medical affairs.
There are also conservatorships.
So, if you want to not be under any of them, make it clear that you can manage your financial, legal and medical affairs. Be ready to prove it. The group that whitewaterwoman linked would probably help you do that.
Looking less child-like
Do you wear cute designs or like animated shows? For meeting with the attorney and judge, I would consider not actively showing those sorts of things if so. If you have any soothing habits like bringing stuffed animals or fingersucking, I would also consider if you can get through at least those two items without it or by hiding it in a pocket or professional bag.
It's up to what you think is best, but those changes can help.
I've noticed that my tendency to enunciate has accidentally caused people to think I'm smarter than I am. Those might help you, along with standing up straight, making eye contact as well as possible, and some other tricks.