One area in which equality between gay and straight people is a given is age: We’re all getting older, and for some seniors (or near-seniors) advancing age equals advancing invisibility.

That’s sadly true for the three autumnal subjects in “Before You Know It,” a bittersweet documentary that follows three gay men in different parts of the country who feel time and change breathing down their necks.

Filmmaker P.J. Raval expertly interweaves all their stories, including that of septuagenarian loner Dennis Creamer, who waited most of his life to come out as a cross-dresser yearning for gay relationships. He’s a sweet and quiet man, somewhat adrift and estranged from his family; nothing much seems to pierce his sad isolation.

There is also Robert Mainor, the sardonic, larger-than-life owner of a gay bar in Galveston, Texas. Every inch a community leader, Mainor is proud of the oasis he has built for drag queens. Unfortunately, we watch some of the wonderful bombast and life go out of him as illness and legal troubles take a toll.

Finally, there’s Ty Martin, a gay-rights advocate in Harlem who is certainly aware of anti-gay rhetoric arising in his community’s churches. We see Martin anxiously talk to people on the street about LGBT seniors, and how he gets a warmer reception than expected.

During filming, New York’s marriage-equality law passed, leading Ty to believe he and his partner will soon get married.

As with everything else in this film, destiny has other plans.

Tom Keogh: tomwkeogh@yahoo.com