The generation born from 1947 to 1949 is seen as members of the first baby boom.
With about 8.06 million members, it was far larger than all other generations.
They grew up at a time when Japan's postwar economy was rapidly growing, and also felt the sting when the bubble economy burst.
They created elements of popular culture such as folk and rock music, manga and fashion, and they are now redrawing the conventional image many people have of growing old.
In 2020, people of this generation will have turned 70, a milestone that presents new challenges for the nation's social security system.
In August last year, legendary baseball pitcher Choji Murata took to the mound at Chiba Lotte Marines' home ground of QVC Marine Field to throw the opening pitch in the "legend series."
Murata, who racked up 215 wins as a pro player, went into his pitching position, leaned back to put his weight on his right leg, lifted his left leg up high in his familiar "masakari" style and unleashed a pitch clocked at 135 kph.
"Until I was 60, I said 'I could throw at 140 kph,'" Murata, who was wearing a retro uniform for the event, said to a Yomiuri Shimbun reporter. "Now, I'm down to 135 kph. But I don't want people to say, 'Ah, but he used to throw faster.'"
Murata, 64, took a hard ball out of his bag. "Get ready to catch this," he said. From a distance of about five meters, he threw the ball and hit a target with great accuracy.
"Youth is not a time of life. It is a state of mind," Murata said, reciting a line from the poem "Youth" by American poet Samuel Ullman.
Since retiring from pro baseball, Murata has thrown himself into projects that include helping middle school baseball teams on remote islands prepare for the national tournament.
"Helping the next generation of baseball players improve is how I repay what pro baseball has given me," Murata said.
Men of the baby boom generation have an average life expectancy of 79.94 years, while for women the figure is 86.41 years.
As Japan stares down the barrel of a super-fast aging society, many of these baby boomers find themselves having to take care of their elderly parents.
Akio Yasunaga, 66, lives in the Tokyo metropolitan area with his wife, 70.
His mother, 94, has been living with them since a 2011 fall that required hospital treatment. His wife was later found to have cancer, so Yasunaga now takes care of both of them by himself.
Yasunaga wakes up at 4:30 a.m. to make breakfast for his wife and mother, and, after helping them eat, comes to his office at 8:30 a.m. In the evening, he does the shopping and arranges to have other meals delivered. On weekends, Yasunaga ferries his wife and mother to the hospital.
An employee at a trading firm, Yasunaga reached the retirement age of 65 in 2012.