Growing up, our grandmas would tell us how girls age faster than boys. We would be playing cha baba and cha mama with our neighbours' kids of our ages, brothers and cousins and those small boys were literally mentally young, however old we knew they were. It came out well in the roles they played in that kalongolongo. The girls had more responsible roles than their male counterparts.
Even when introducing ourselves to visitors and those annoying relatives who pretend they didn't know or remember us, we often heard remarks like "and she's (the girl) so grown she even looks older than her elder brother'. Such remarks would really annoy us.