I'm the family cruise editor here and just sailed on the Zuiderdam with my family in March. We loved the ship (we have two children) -- great service, good food, and attractive, energetic decor. The ship does seem to be more geared towards families and older couples. (There won't be as many families on the ship in Sept since it's back to school month.) However, there is a disco, nightly shows, etc. for younger passengers like yourself. We met up with some parents in their early 30s who would have liked more action at night than there was on the ship. (We have a toddler who is up at 5 or 6 a.m. so we were happy to go to bed early instead of hanging out late!)
As for tipping, you don't have to tips as much on HAL as other ships, however, the waiters and stewards do seem to get smaller, additional tips from pax. We did give them some money at the end of the cruise -- they were very gracious and efficient and truly deserved it.
Let me know if you have more Q's.
Luisa Frey Gaynor