While the Oceaneers Club/Lab is for ages 3-12, there are two areas within the space. Oceaneers Club has activities aimed at the 3-7 group, while Oceaneers Lab has activities aimed at the 8-12 group.
That being said, any child in the Club/Lab space can participate in whatever activities appeal to them, regardless of age.
I will also point out that there really aren't that many 11-12 year olds in there, as they usually go to Edge (11-14).
The terminal at PC was built during the time that the classic ships were the only ships DCL had. With the advent of the newer, larger, ships, the terminal was too full with all the people who wanted to "be there when the port opens, and first onboard". The fire marshal said something had to be done. What was done was having people select a PAT in order to space out the numbers of people in the terminal.
Staterooms are ready around 1:30. Remember, the prior cruise, everyone was off at 9:00 (or so DCL hopes). That only gives the room hosts (as well as all the other CMs onboard) 41/2 hours to clean/reset the rooms for the next cruise. Many times this involves some pretty deep cleaning, as well as, in some cases, even switching out mattresses, etc.