I've read that Holland America has become less of a cruise line catering only to seniors but in our trip 8 out of 10 people were seniors. It was great for us because there were no loud noises, children running up or down, and especially we loved that the music played in the bars and lounges was calm and not loud to the point of hurting your ears as in other cruises so we really enjoyed that part. Also the AC wasn't freezing cold as in all the other cruises I've taken. Stateroom service is also incredibly silent and we noticed our clean room but never the cleaning crew except the main cabin attendant who asked if we needed anything when he met us in the hallway.
My only complaint noise-wise is that the public announcements can't be muted. They sound "only" in the hallways but are loud enough to be heard by an older person in the shower. They start with a chime and then instead of just informing people could now get out of the ship the cruise director went on an on and on about activities for the day at 7:00 am! This made it impossible to sleep in and sometimes nap since she did the same for departure. Not everybody care for those announcements so I think they should sound inside the room and not just the public areas but allow for volume control.
As for the ship, the Maasdam is the second smallest ship in HAL's fleet so you should expect the basics of all cruise ships but smaller. However, it does have a wonderful, vast library with books for every interest (only problem is that it's the coldest area in the ship), a daily summary of news and a coffee shop (extra charge).
Cabin 644 was excellent. Very quiet despite being bellow an open veranda hallway that's the "balcony" of the lanai staterooms upstairs but can be publicly accessed. It was close to the stairs and elevators that took you right to the dining room and the lido buffet without being too close to have any noise from it.
The room was nice with a sofa bed and a small tub in the bathroom. Window is very nice and large too with perfect views. Highly recommended room. Also, since it's on the bottoms floors and close to the center of the ship the rocking of the ship was less noticeable than in other areas of the ship.