Something things to think about.

Post 546 - Here are some things I found out last week, both good and bad, to think about:

Teenagers aren't necessarily tuning out adults these days; they simply might not be able to hear them. The proportion of teens in the United States with slight hearing loss has increased 30% in the last 15 years, and the number with mild or worse hearing loss has increased 77%, researchers said last Tuesday. One in every five teens now has at least a slight hearing loss, which can affect learning, speech perception, social skills development and self-image; one in every 20 has a more severe loss.

One-third of people in their 20s move to a new residence every year. Forty percent move back home with their parents at least once. They go through an average of seven jobs in their 20s, more job changes than in any other stretch. Two-thirds spend at least some time living with a romantic partner without being married. And marriage occurs later than ever. The median age at first marriage in the early 1970s, when the baby boomers were young, was 21 for women and 23 for men; by 2009 it had climbed to 26 for women and 28 for men, five years in a little more than a generation.

Sociologists traditionally define the “transition to adulthood” as marked by five milestones: completing school, leaving home, becoming financially independent, marrying and having a child. Among 30-year-olds in 2000, according to data from the United States Census Bureau, fewer than half of the women and one-third of the men had done so. A Canadian study reported that a typical 30-year-old in 2001 had completed the same number of milestones as a 25-year-old in the early ’70s.

People can vote at 18, but in some states they don’t age out of foster care until 21. They can join the military at 18, but they can’t drink until 21. They can drive at 16, but they can’t rent a car until 25 without some hefty surcharges. If they are full-time students, the IRS considers them dependents until 24; those without health insurance will soon be able to stay on their parents’ plans even if they’re not in school until age 26 (or up to 30 in some states). Parents have no access to their child’s college records if the child is over 18, but parents’ income is taken into account when the child applies for financial aid up to age 24. We seem unable to agree when someone is old enough to take on adult responsibilities. But we’re pretty sure it’s not simply a matter of age.

A longitudinal study of brain development sponsored by the National Institute of Mental Health, started following nearly 5,000 children at ages 3 to 16 (the average age at enrollment was about 10). The scientists found the children’s brains were not fully mature until at least 25. “In retrospect,” according to Jay Giedd, the director of the study, “the only people who got it right were the car-rental companies.”

It took radio 38 years and television 13 years to reach audiences of 50 million people, while it took the Internet only four years, the iPod three years and Facebook two years to do the same. It's no surprise that fewer than 100 of the companies in the S&P 500 stock index were around when that index started in 1957.

Back in the Ordovician period, the earth spun so fast that days were only 21-hours long. With three fewer hours each day, people arrived at old age sooner. But age is better than extinction. The history of human life on this planet has been punctuated by many extinctions. The great Permian Extinction of 250 million years ago was so catastrophic that life was almost brought to a close. Today, many people feel that a comparable man-made extinction is in reckless progress.