By Mandy Oaklander
February 12, 2015

As sudden as aging can feel, no one wakes up in a 90-year-old body without getting some warning signs first. But if you know what’s coming, you can plan to give certain parts some extra care early on. Already in the throes of aging? (Trick question. We all are.) “You’re never too old to do anything to help to maintain wellness of your body,” says Dr. Ronan Factora, geriatric-medicine expert at Cleveland Clinic.

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Age when body part begins to falter

40 EYES

Your eyes begin “like a multifocal camera,” says Dr. Rachel Bishop at the National Institutes of Health’s National Eye Institute, but by age 40, range of sight declines. To prevent eye disease, don’t smoke, and wear sunglasses to keep out UV radiation; sun exposure and smoking accelerate cataract formation.

40 MUSCLES

All of us lose muscle and gain fat as we age, says Dr. Luigi Ferrucci, scientific director of the National Institute on Aging. That sad trade-off picks up at age 40. “You need to absolutely insert exercise activity in your routine if you want to avoid muscle decline,” Ferrucci says.

35 BONES

Bone mass tends to go downhill at a rate of up to 1% per year after age 35 (and faster after menopause). Weight-bearing exercise makes a big difference in bone density. A 2015 study found that simply jumping 20 times twice a day significantly improved hip-bone mineral density.

30 LUNGS

Lung function begins dropping 1% a year at 30 and declines more in people who are sedentary than in those who are active, says Dr. Thomas Perls, geriatrician and principal investigator of the New England Centenarian Study at Boston Medical Center. The antidote: exercise.

18 SKIN

From around 18, resilient collagen and stretchy elastin decline at about 1% per year. You can slow the process by not smoking, eating well and wearing titanium or zinc sunscreen every day–even if you’re indoors. A 2012 study found that some compact fluorescent bulbs emit skin-damaging UV light.

70 BRAIN

You don’t lose your mind all at once–but by 70 you’ll start to see age-related brain changes speed up, says George Rebok, a cognitive-aging researcher at Johns Hopkins Bloomberg School of Public Health. Stick with activities that engage and stimulate you, he says.

60 EARS

Age-induced hearing loss happens gradually, but 1 in 3 people ages 65 to 74 has it. There’s not much you can do to slow it, but listening to or playing lots of loud music or working in noisy industries like construction will hasten it, says Boston Medical Center’s Perls.

65 HEART

As you age, your heart-muscle cells shrink in number but expand in size, which makes your heart wall thicker. Your arteries tend to get stiffer too. Starting at age 20 to 30, peak aerobic capacity drops by about 10% per decade, and heart disease typically kicks in around age 65.

50 KIDNEYS

You won’t necessarily feel it, but decline in kidney function starts around 50. The best thing to do is drink plenty of water. Since thirst decreases with age, you may have to remind yourself. One study found people who drank the most fluids were less inclined to kidney decline.

60 GUT

The hairs on your head aren’t the only strands to go. Villi in your intestine–tiny hairlike projections that absorb the nutrients in food–tend to flatten out around age 60, says Cleveland Clinic’s Factora, and the loss means you’ll absorb fewer nutrients.

Write to Mandy Oaklander at mandy.oaklander@time.com.

This appears in the February 23, 2015 issue of TIME.

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