Hence, according to any opinion, Dinah would have to have been a minimum of 8 at the time.
any opinion that you looked at, not exactly any opinion
Dinah was older than Yosef [as we know from Chumash, where Leah prayed for her 7th pregnancy not to result in a son since that would shame her sister Rachel].
they were the same age the reason Leah davened she should have a girl was because they were both pregnant at the time and Hashem switched both fetuses (however you want to learn it)
I’m sorry I’m in the process of moving so all my sefarim are in boxes right now, but will try to find sources in yeshiva and write them down