Growing up in the Iowa farm belt, Dr. Loren Olson always thought of himself as "heterosexual, with a little quirk."
He wondered why he had to work so hard at masculinity and attributed his feelings of being a "man-imposter" to the death of his father in a tractor accident when he was 3.
Olson went on to have a satisfying 18-year marriage and two daughters but, inside, he always knew something wasn't quite right. He describes "always editing my behavior and thoughts." But long after many men acknowledge their sexual orientation, he came out after the age of 40.
In his new book, "Finally Out: Letting Go of Living Straight," Olson, now 68 and semi-retired psychiatrist, examines the lives of closeted gay men, many of whom have sex with other men but deny they are homosexual.
"These men lead hidden lives and that's a very lonely place to be," he said. "They feel like they are one secret away from losing everything they love." Olson describes it as "a kind of sexual purgatory," and many turn to drugs and alcohol for solace.
In 2007, when Republicans distanced themselves from former Idaho Sen. Larry Craig after he was arrested in an airport bathroom in a sex sting operation, Olson was horrified.
"I felt personally attacked," he said. "In many ways, Sen. Craig is the same age and from the same kind of community and same period of time as I am. The important thing [Craig] said is, 'I am not gay,' but he didn't say, 'I did not have sex.'"
A 2006 study that was published in the Annals of Internal Medicine revealed that 10 percent of men who called themselves heterosexual have had sex with men, many of them married.
Olson's book weaves memoir with an online survey of 132 men who have sex with men. In seeking responses, he intentionally didn't use the word, "gay." He provides insight into their mindset and sexual habits: They avoid the intimacy of kissing and anal sex in their relationships.
"My sexual attraction, behavior and sex identity are all in alignment," Olson said. "Many men struggle to line these three things up in a way that gives them peace and comfort."
Olson also noted a real "disconnect" between the older and younger generation of gay men.
"There are a lot of really out and proud gay young men, but they don't know we exist or they don't really sense that we are authentically gay," Olson said. "They think we should have figured it out or are intentionally hiding and don't have the guts to come forward as they did."
The average age at which gay men come out has fallen steadily in four decades, according to a 2010 survey by the British LGBT group Stonewall. In the 60-plus group of those who had already come out, the average age was 37. For men and women in their 30s, the average age was 21 but it was 17 for the 18 to 24 age group.
Gays, lesbians or bisexuals who reveal their sexual orientation typically boost their self-esteem and experience less anger and depression, according to a 2011 University of Rochester study.
But men who come out in middle age face other barriers: financial insecurity, social isolation and being childless or estranged from their families, according to Judy Evans, a spokeswoman for the group Service and Advocacy for GLBT Elders (SAGE).
"These older Americans came of age at a time when being gay was labeled a psychiatric disorder and there was overt discrimination," Evans said. "They are really not used to living lives so openly as the younger generation."