We travelled as one of 4 couples - of the eight of us, we were the only Silversea/cruising novices. Turns out many of the passengers were returning guests, and/or planned to book again on the Silver Explorer for future expeditions.
We had expected to be the youngest passengers (we are in our 30's) but there were several families with children, and numerous passengers of our own age.
Our cabin was on the 3rd deck, so I believe it was relatively stable. Nevertheless I am sensitive to motion and was quite seasick, despite enjoying "Drake Lake". Rather than eat up at the restaurant, my butler was frequently able to arrange for me to have whatever dish I wanted served in my cabin. A much appreciated benefit of the butler service!