The thing is, you don’t get to decide that it’s okay to call people something they don’t want to be called. I don’t like being called a girl. Most women I know don’t like being called girls. Whether or not you meant it that way is not super relevant. See:
Intent is Important, but Impact Matters More
Why you need to step up and recognize the repercussions of your speech and actions
You can compliment someone without calling them a girl. You can say, you look lovely or you seem happy or it’s nice spending time with you or I enjoy your company. Saying you address women as girls as a subliminal message that they look youthful is really gross to me. I don’t want men trying to put ideas in my head by using subliminal language. Whether or not you think you were alluding to lack of maturity, the reality is that “girl” has a specific definition and it isn’t the same as “woman.”
“Menarchy” isn’t really something you need to be considering. There is no such thing as an underage woman. How the heck would you know if someone had gone through puberty anyway? It’s not like you can tell that they’ve menstruated by looking at them, so I’m not sure why that is even in play here.
Whether you have attached significance to these terms isn’t really relevant, because you have to listen to women about what they want to be called. You don’t get to make that choice for us. Just because you have never attached a certain meaning to something doesn’t mean other people aren’t. Just because you are ignorant doesn’t mean you are right, or excused.