I think when I was younger, I was better at understanding women. Or maybe the genders are less different when you're younger.
Then once I got married, I found it harder to understand women. Big weddings, nesting, the biological clock... it's something I can intellectually understand, but it's not something I truly get.
So I would say, I don't really understand women as well as I thought. Maybe 50%? That's a failing grade though.
Do you understand the opposite gender? How has that changed (or not) over time?
ETA: Also, are your siblings of the opposite gender or the same?