All my cockerels and pullets (but 2) are about 18 weeks old yet. I think it will be a few more weeks but my little hormone crazed boys have been riding my girls for about a month and even attempt each other if I have the girls locked up. They also jump on my 2 littlest ( 10 weeks old) girls. I'm thinking it doesn't make any difference if the girls are ready to lay or not.
You are correct. It doesn't matter to them, how old the ladies are.