Princess draws a pretty broad spectrum of ages. I met several single 30-something ladies (a situation that a 43-year-old bachelor does not exactly lament!) and married couples who seemed to be even younger, along with people who were well into their 80's and at every age in between. Since the Halloween sailing did occurred while schools are in session, there were not very many school-age children. Nonetheless, there were several families with pre-school children.
The bottom line is that you probably will meet people of your own age on any Princess cruise -- whatever "your own age" happens to be!