In my area, OKCupid and Plenty of Fish aren't too great, but that's only because of the selection pool. Your area might be great. Tinder is more of a hookup app, but it's very age-centric in the extreme.
Me - male, 42, poly, straight, in a serious relationship with Audrey, also casually dating.
Audrey - female, 20, poly, pansexual, also casually dating.