Sleep schedules often change with age. That's why teens are known for sleeping until noon, while retirees often wake up before the sun.

If you're getting tired earlier than you want to be, you may be able to blame biology.

Circadian rhythm is the natural process bodies use to control the timing of functions like sleep and appetite. Work schedules, exposure to light and other environmental factors influence this internal sleep clock.

Your circadian rhythm is also responsible for age-related sleep changes. Here's how it can affect different age groups:

Babies. Babies start to develop circadian rhythm around 6 weeks of age. Their sleep clocks tend to get more reliable between 3 and 6 months.

Children. Kids' sleep clocks are usually set early. As a result, children under age 12 often wake early in the morning — as parents who want quiet time at 6 a.m. know.

Teens. Puberty changes teens' internal clocks. It delays the time they feel sleepy at night and the time they naturally wake in the morning. This is why it's difficult for teenagers to fall asleep at an appropriate time to get up for school in the morning.

Adults. After age 20, the internal clock starts shifting earlier, so adults tend to get tired earlier at night and wake earlier in the morning.

Women's clocks are typically set earlier than men's in the younger adult years. Women tend to be more alert earlier in the day and get tired earlier than men. After about age 50, men's sleep clocks seem to shift earlier, so men get tired and wake up earlier than women.

Older adults. Adults over 65 see their clocks shift even earlier than younger adults. They also spend more time in light and less restful sleep stages.

Older adults may have trouble falling asleep at night, wake up in the middle of the night or wake up before they feel fully rested. They tend to take more daytime naps to make up for their altered rhythms.

Reset the clock

A few sleep tips could help you reset your clock, so you can rest on your own terms:

• Get outside. Regular exposure to sunlight can help keep your internal clock on track.
• Stick to a schedule. Try to go to bed and wake up about the same time each day. Sleeping in on the weekends makes it more likely that you'll have trouble falling asleep at night.
• Avoid long naps. If you feel drowsy during the day, a midafternoon nap of no more than 30 minutes might help. But if you have trouble falling asleep at night, daytime napping can worsen the problem.
• Be active. Exercise may help you fall asleep at night and sleep more deeply.
• Curb the caffeine. Avoid caffeine after 3 p.m. This includes coffee, tea, soda and energy drinks. Caffeine can interfere with a good night's sleep.
• Avoid heavy eating before bedtime. If you're hungry, a light snack is best.
• Know when to unplug. Put away all screen-based devices a half-hour before bedtime. Screen-based light can increase alertness and decrease sleepiness. When possible, keep devices out of bedrooms to prevent late-night disruptions.
• Keep it calm. Wind down 30 minutes to an hour before bedtime by taking a warm shower, reading a book or doing other calming, quiet activities.

If you've tried the steps above and you are still having trouble sleeping, talk to your health care provider. Your doctor might be able to check you out to see if a sleep disorder is getting in the way of restorative rest.