I used to say "guys" to refer to everyone all the time but I've recently tried to stop. I don't know why I decided to stop. I think it's because when I got older and started to be on the same level as other women ( and not just other kids) I didn't want to call those women "guys". Idk, it does come out occasionally out of habit though.
It's true that men are rarely refered to in a serious way as "boys". I remember being younger and getting a lecture about not calling men "boys". However, I never received a lecture on not calling a woman "girl". It's definitely a double standard. Either way, I try to use "ladies" most of the time.