Thirteen. And I had to tell him to change and bring that pair back down so it could be washed.
Luckily he didn't just take them off and hand them over right then.

That would have really irked your daughter, which most little brothers love to do.
Anybody out there go "Commando".
Ever see There's Something About Mary?
Just gotta watch that zipper!
When we were kids, my brother wore the same dress socks day after day, night after night. When he finally took them off, his calves were brown!
I used to wear my underwear several days in a row, but now I change it every day. In fact, I change everything except that, on weekends, I'll sometimes wear the same pair of pants two days in a row. I used to dread doing laundry, but I pretty much enjoy it now. I don't iron, tho--I take my shirts straight out of the dryer and hang them up. If I sound like too much of a neat freak, well ... you should see my apartment. We can euphemistically call it bachelor style. I am getting better about washing the dishes. I do that every day instead of letting them pile up in the sink.
By the way, am I missing something with the famous Mary scene? Everyone else in the theater, including my date (a guy) was laughing hysterically. I am doubled over in vicarious pain. Just thinking about it makes me cringe.
Anyway, I don't know if I keep up with all the "guy things" (definitely not into sports, except to admire the athletes ...), but I'm a guy.