From NCL Website FAQs:
"How should I dress for dinner?
Freestyle Cruising gives you the freedom to dress as you please – morning, noon and night.
Casual attire is perfect for all restaurants during the day -- Khakis, skirts, jeans, casual tops, shorts or whatever. Swimwear with a cover-up is fine at the buffet and outdoor restaurant.
For dinner, collared shirts and pants or nice jeans work for guys. Slacks or jeans, dresses, skirts and tops are perfect for women. But if you want to dress up and add a little glamour when you dine out, that’s OK too – we’ve reserved one restaurant each night just for that.
For kids 12 and under, nice shorts are appropriate in all restaurants at all times."
Looks like 12 and under are now allowed to wear nice shorts.