Whatever you might hear from reality shows, where some guy has multiple 20 something girlfriends, the truth is that plenty of poly people are 1) older and 2) married or gone through a divorce.
The younger poly community also tends to be more dating focused, rather than relationship building focused. At least from my personal experience. My theory is that it takes time to get accustomed to something like poly and people are more ready to commit later in life.
So I'd say dating in your 40s and 50s is in some ways easier than dating in your 20s
At least, assuming you want something long term.