I was on the Caribbean Princess in March.
Skywalkers is a really nice looking club and actually I didn't see any underage teens there.
The teens were all in the Teen Disco and as soon as they tried to get into Skywalkers they were refused.
Some girl we met was also refused to get into the skywalkers club while she was 19 years old. After some discussions she finally was allowed in.
The first night of the cruise Skywalkers was great, many people inside the club and on the dancefloor.
The second night was a little less crowded but still good enough for a great time.
After that it went more quiet every night, so we thought everybody would be there at the last night before getting off the ship.
Nope... we were about the only people around hehe, so it was kinda a fluke that day.
I really don't know how it would be when you're there, but I'm sure you can at least enjoy Skywalkers 2 or 3 times during your cruise,.
I think the ages of the Skywalkers club varied from 18 years to 30. I haven't seen many people above 30 up there, except of some bartenders.
Always make sure you have your ID with you, otherwise you can go back to your cabin