Hi Mike, and welcome to cruise-chat.com.
The Freestyle Dailies for N. Pearl do indeed note that the Bliss Ultra Lounge is, after 9:00 pm, for pax ages 21+. I don't know how they enforce it once the clock strikes 9:00. The other lounges do not have this restriction, as far as I can tell.
Also, if you or your TA haven't done so already, you need to familiarize yourselves with NCL's age policy
, particularly the parental consent letter that may be required for boarding.