Technically, the brain doesn't finish developing until 25 or so
(so there isn't much hope for me anymore lmao...)
18 is not any magical age, honestly, because like others have already stated in this thread, you will never stop growing and maturing.
The works you make at 18, or 25, or 40, will be probably technically superior to what you can make now - but they'll be also very different, and might resonate with different audiences, for different reasons. Everything you create is a stepping stone, and everytime, you'll think "wow i really could have done that thing better" about your older works, and that's fine.
Don't worry about your age or maturity, just work on your comic with the time you have now and publish whenever you feel prepared!