We took a cruise last year on the Grandeur of the Seas and my son was only 11. We were able to sign a waiver stating that we allowed him to be in the 12 yr (teen) program. He loved it!! We had no problems. Enjoy!!
I have gone on one NCL cruise back in 2012 (the Gem or Star or something like that) and while the experiences are somewhat similar, I felt NCL suffered more from upcharging more than RC does.
I also felt the RC crew were a bit more attentive than on NCL.
Again, I'm no NCL expert and I haven't sailed on their newer ships.
What I always tell folks when it comes to comparing RC to other cruise lines is I feel RC offers the right balance of what you pay for versus what you get. Other cruise lines offer more than RC does, but they also charge much more. Some cruise lines are much cheaper than RC, but it feels like that comes at a price of what you get.