If only a man's physique could morph through its growing pains as obviously (and awesomely) as Bruce Banner's when he transforms into the Incredible Hulk. Alas, comic-book science doesn't conform much to actual science, leaving the average-dude antihero with little to go on when it comes to knowing how the body ages and more importantly, exactly when a change is gonna come.

Fear not, mere mortal. Modern-day medicine has come a long way in helping us understand the aging process in a number of ways, from the vain (wrinkles and jowls) to your veins (keep 'em plaque-free and you can feel like a boy of 30 for decades to come). Science may not have answered some of the most nagging questions (why do your nose and ears get bigger as you get older?), adhering to these 20 age-specific signposts that follow will greatly increase your chances of becoming the sprightliest superhero at the senior citizens' center.

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Ages of Men
Find out more scientific facts about what a man can expect from his eyes, teeth, hair and more as he ages. Click here to see the 20 big stages of a man's life.
Mario Tama, Getty Images
Phil Walter, Getty Images

20 Big Stages in a Mans Life

    Age: 9 to 15-ish -- Time to man up

    Science shies away from saying exactly when you become a man, though research has shown that, while girls hit puberty first, both genders are going through it sooner than they did perhaps even a generation ago. For guys, pubic hair growth tends to come first, followed by armpit hair growth and odor. The scrotum becomes thinner and redder around age 12, the penis and testicles start growing around age 13 and that Peter Brady-style cracking and deepening of the voice usually begins at age 13-and-a-half. By the time you come out the other end, you'll have developed pecs and delts, likely gained a few inches in height and probably need to start shaving. Welcome to the big leagues, buddy.

    Everett Collection

    Age: 17 -- You've got a smart mouth on you

    Wisdom teeth typically "erupt" (dentist-speak for the surfacing of a new tooth) around 17 or 18 years of age. Should you never get yours, however, that doesn't make you a moron. Rather, you're on the cutting edge of evolution. "You have to have a tooth bud at birth in order to later have a tooth, and as heads and jaws have become smaller since Cro-Magnon times, we see a small percentage of people born without wisdom buds," says Dr. Mario Vilardi, a periodontologist based in Fishkill, New York, who publishes the quarterly magazine Dear Doctor Dentistry and Oral Health.

    vanberto, Flickr

    Age: 18 -- It's flossin' season

    This is also the time when your get-out-of-flossing-free card expires. "Up to about 18, there seems to be a protective immunity to gum disease for most people," Dr. Vilardi says, "then we start to see vulnerability." To ward it off, floss before you brush, then follow up with an antibacterial mouth rinse for 30 seconds.

    Archie McPhee Seattle, Flickr

    Age: 20 -- "I am, I am, I am Superman"

    Many stats show that a man's at his physical peak upon entering his third decade of life. At this age, your hair follicles are at their thickest, your eyesight's at its sharpest (if you haven't yet had the need for contacts or glasses), you're having the most orgasms of your life (though you're also having the most alone-time orgasms of your life) and your spinal discs are receiving optimum blood supply to ward off injuries. Congratulations. Go upturn a Mini Cooper, just because you can.

    Everett Collection

    Age: 25 -- Not so quick on the draw

    As recently noted in the book "You Staying Young: The Owner's Manual for Extending Your Warranty" by Drs. Michael F. Rozien and Mehmet C. Oz, hand-eye coordination can start to lessen as early as age 25 thanks to a slowdown in the synapse-firing between your brain and your body. In other words, biology is telling you that maybe it's time to give up the video games already. (And if it's your girlfriend telling you so, she may be right, too: Studies have shown that men are more likely to lose the ability for complex problem solving as they age.)

    JFourNames, Flickr

    Age: 28 -- The lines start here

    Approaching 30, you might find that lines on your forehead stick around even after you've finished berating the intern with brow-furrowing rage. No problem if you want to pursue the George Clooney, distinguished-gentleman look. Otherwise, Dr. Jeffrey Benabio, a fellow at the American Academy of Dermatology, recommends combating such fine lines by using "any regular moisturizer at night, and an over-the-counter, salicylic acid peel once a week."

    Getty Images

    Age: 30 till you croak -- Andropause and effects

    While the phrase "male menopause" (aka andropause) has fallen out of favor among many in the medical community, "there is an age-related phenomenon that affects both men and women where the body produces lower amounts of hormones, affecting how they feel, their sexuality, and their sense of well-being," says Dr. Abraham Morgentaler, author of "Testosterone for Life: Recharge Your Vitality, Sex Drive, Muscle Mass and Overall Health." In other words, that hormone decrease that's also causing your sarcopenia. Whereas females experience a sharp drop in hormone levels later in life, men's andropause is long-lasting and gradual. But both can ultimately lead to depression, chronic fatigue and osteoporosis, and both can be treated with hormonal therapy.

    PracticalOwl, Flickr

    Age: 30 -- Hardcore no more

    Mother Nature gives the average male sarcopenia for his 30th birthday. That's the loss of muscle mass, and you can't ever regift it; it's due to the body producing less testosterone, and the decrease is continuous from here on out. But you can start strength and resistance training in order to build yourself back up.

    Hulton Archive / Getty Images

    Age: 31 (and up) -- More bad news about your gum-ga-gum-gum-gummmmsss ...

    Prior to 30, the major cause of tooth loss is decay (i.e., cavities), but after 30, "70 percent of tooth loss is due to gum disease," says Dr. Vilardi. Why we're telling you this again: Because when you don't floss away food debris between your teeth, that food combines with your saliva to create bacteria, and the bacteria release chemicals that seep into your bloodstream via the "pocket" between your gum and your tooth, and research is showing more and more that this is perhaps the major -- and certainly most preventable -- cause of heart disease, heart attacks, strokes and possibly even cancer. Plus, you will lose your teeth and no woman will want to kiss you. Have you started flossing yet?

    Mario Tama, Getty Images

    Age: 34 -- Cancer rising

    According to the National Cancer Institute, this is the median age for testicular cancer diagnoses in the U.S., but many experts note that men in their mid-20s are considered most at risk among the 18-to-40 set. The good news: It's one of the most curable forms of cancer, with remission rates above 90 percent. The maybe not-so bad news: "The most common way to check for testicular cancer is not at an annual physical, but by conducting monthly self-exams," says Dr. Taylor Hays, chair of the general internal medicine division at the Mayo Clinic. Best to do it after a shower, when the scrotum is looser, and schedule a visit to the doc if you detect anything down there that isn't smooth to the touch, like pea-sized lumps, ridges or overall rigidity.

    Dave Etheridge-Barnes, Getty Images