For 50+, Facebook is a great platform, as you mentioned. Another one that still does well with 50+ is print, either in your daily newspaper, or magazines. It would depend on the behavioral targeting you're looking for, but print readers are typically 50+ and more affluent.
In addition to Facebook, I would highly recommend utilizing the Google Display Network with targeted campaigns in a number of areas such as healthcare, travel, & finance.
I'm a true believer in direct, real world marketing when ramping up growth. Active Living communities are exclusive to ages 50+. Collaborate with the developers of these communities in order to engage homebuyers and/or residents. A strategic plan for sustainable growth is just 1 call away.
You can use Instagram and LinkedIn to reach 50+ people as a demographic. Use the advance settings in the ad placement.
Please note that it is costly to run ads on LinkedIn.
Honestly, I would explore direct mail!