The new age of adulthood: 30. Our extended adolescence has really, well, extended. But according to Josh Albertson, Lockhart Steele, and Jonathan Van Gieson, authors of the “Book of Ages 30,” life begins at 30. Thirty is cool. That should be good news to the 3.8 million Americans who will turn 30 this year. Unlike their parents, today’s thirtysomethings think of this milestone as a new beginning and not an end. Priorities shift. New things become important. Uh oh. Your adulthood is showing. So who are America’s thirtysomethings and what do they have to look forward to? “Book of Ages 30” has an interesting take on it:

How old is 30?
if you’re 30, you’re old — specifically, you’re older than 42% of all Americans. But you’re not alone. Fifteen% of Americans are also in their 30s.

The good, the bad, and the ugly of being 30
if you’re 30, you’ve already lost 10% of your muscle mass. You’re likely to be in debt to the tune of $20,000. But the good news is that you’re also likely to be having sex 2.24 times a week.

while 81% of women and 71% of men have been married by their early 30s, there are plenty who are still virgins after their 30th birthday: 1 in 33 men and 1 in 25 women.

Your good looks
Men at 30 are on average 5′ 10.2″ tall and weigh 174 pounds, while 30-year-old women are 5′ 4.6″ tall and weigh 130 pounds.

Let’s talk money
The median income for 30-year-old men is $30,510, while the median income for 30-year-old women is $21,473. On average, 30 year olds have held 7.5 jobs. They have a 24% chance of being promoted in the next year.

Career peaks and valleys
J.K. Rowling published the first volume in the “Harry Potter” series just before she turned 32. By 30, Harrison Ford went from being a carpenter to an actor in “American Graffiti,” and back to being a carpenter. Remember Mr. T? At age 30, in case you wondered, he was about to play the villain in “Rocky III.” When they were 30, no one other than their family and friends knew who Oprah Winfrey or Jane Austen were.

No more naps
You’re less likely to fall asleep at your desk than those young twentysomething whippersnappers down the hallway. Just over half of 18- to 29-year-olds report substantial daytime sleepiness, compared with 33% of the over-30 crowd.

Don’t shoot!
Nearly half, 45%, of all thirtysomethings own a firearm. In fact, more people in their 30s own firearms than do people in any other decade of their lives.