Here's everything you ever wanted to know—but thought you were too old to ask.

According to Laura Berman, PhD, author of The Passion Prescription, even sexually savvy adults have questions about penis size (it might matter), sex after marriage (does it stop?), and a man's sexual prime (hint: younger is not always better).

"Sexually speaking, people are on a constant quest to know if they are normal," says Berman. So get out your notebook—anda ruler!—and see how your knowledge stacks up.

Does Size Matter?
There's no definitive, er, yardstick that can be used to measure sexual performance—but size does come into play. "Studies show that sexually satisfied women perceive their partner's penises to be large, while unsatisfied women see them as smaller," says Berman.

But those who are not well endowed can still score in bed. "Men on the smaller side become proficient in other kinds of foreplay, so this helps women have orgasms," she explains. "And in any case, not all women can achieve orgasms from sex."

Anthropologist Helen Fisher, PhD, author of Why We Love: The Nature and Chemistry of Romantic Love, asserts that size is not as important as men think it is. "There are many things other than size that make a difference to a woman—for example, education, health, and careers. Men worried about size need to find out what their partners like, and figure out the right ways to move."

Is Masturbation Bad For Your Relationship?
By now, we've shed the silly suspicions that masturbation causes blindness or hairy palms. But in a committed relationship, it's still sometimes considered taboo.

Solo sex shouldn't be classified as cheating, according to Berman, since it's not harmful to a relationship unless it's compulsive or used as a substitute for intercourse. In fact, it can even help your sex life.

"Women who self-stimulate have higher levels of sexual satisfaction, desire, and interest," Berman says. "It's the 'use it or lose it' phenomenon." Masturbation can also help with sexual dysfunction: women who can't orgasm can learn a thing or two from self-pleasure, while men who ejaculate prematurely can use it to practice control.

Do Single People Have More And Better Sex Than Married Couples?
Experts say that neither group comes out on top. "The optimal amount of sex happens when you live with someone," says Edward O. Laumann, author of The Social Organization of Sexuality: Sexual Practices in the United States, and a sociology professor at the University of Chicago.

"Frequency decreases strongly as you have more partners." As for quality, research has shown that married people also have higher levels of sexual satisfaction than singles, says Berman. "Trust and a connection allow you to safely explore and meet your sexual needs," she adds. "But after 10 years together, satisfaction can decline. So they're not much better off than singles, on average."