I mean, you can. It's like with TLS certificates. The standard is there. The code is there. You can issue your own.
The question is, who will trust you?
Where I think we are not in agreement the question of "who to trust" and "for what purposes".
Are you going to trust me when I tell you that I'm over 18 if I provide you with the document signed by my cousin, Honest Ahmed?
Are you going to trust me when I show you the document signed by my government?
(this is the trick question, you don't have a choice, law says you must; there's a list of who you need to trust and for what purposes; like a certificate root store in your browser)