What men really think about their performance in bed

Early in his career, Dr. Abraham Morgentaler thought he knew everything about world of men and sex before he was baffled by a client.

"A young guy comes in who's a tough stud, not particularly likeable, and within a few minutes, this guys's crying in my office because his concern is his finishing too early to be able to provide pleasure and satisfaction to his girlfriend. I never would have thought that was possible," Morgentaler said Tuesday on "CBS This Morning."

As an associate clinical professor of urology at Harvard Medical School and the founder of Men's Health Boston, he meets with men who suffer a diverse range of issues related to sexual and reproductive health.

He said thousands of his patients have repeated similar stories.

"It's not just about what the guys can do for themselves, it's their sense of masculinity actually comes through by what they can do for their partner," Morgentaler said.

That masculinity, he said, is the "key to who [a man] is."

"The Truth about Men and Sex: Intimate Secrets from the Doctor's Office," is his latest book that aims to break stereotypes he said have plagued men for years.

According to Morgentaler, 52 percent of men between the age of 40 and 70 have some degree of erectile dysfunction and 20 percent of men, regardless of age, have premature of ejaculation.

"It makes them feel terrible," he said.

Morgentaler also said one-third of men over the age of 45 have low levels of testosterone that can reduce a man's desire and sexual function.

To find out how Morgentaler answered the age-old-question "Does size matter?" watch the video above.