This July 30, 2011 photo provided by Rhonda Sarter Gold shows a group of friends, back row from left, Susan Drechsler Rosenzweig, Laurie Stoller Birzon, Alice Sohne Meyer, Jodi Wechter Levy, Karen Silpe Morgenstern, Jill Hirschhorn Gordon and front row from left, Rhonda Sarter Gold and Sharon Stutman Miles, in New York after one of them proposed a reunion for their 50th birthday. Many baby boomers are marking milestone birthdays in a big way, with communal celebrations and elaborately planned parties.

NEW YORK — It started with an e-mail to a couple of friends: “Do you want to meet in Manhattan for our 50th birthdays?”

Before she knew it, Amy Delman and more than a dozen women — some of whom hadn’t seen each other since high school graduation in 1979 — were coming in from around the Northeast for a weekend in the city.

And when they finally got together, they found that they shared not just childhood memories going back to second grade, but also the need to take a deep breath and take stock of their lives in middle age.

“It’s almost like a new beginning,” said Delman, who grew up in Jericho, Long Island. “Our careers are set, our kids are grown, some of us have lost a parent. It’s a sense of ‘Wow, I’m not a kid, I’m not young, I’m in middle age, but I want to enjoy it and not have any regrets.”’

Many boomers say they are marking the milestone birthdays of middle age — 50 for those born at the tail end of the post-war Baby Boom and 60 for those born in the early 1950s — in a big way. They’re jumping out of airplanes, reuniting with lifelong friends for communal celebrations and toasting the decades at elaborately planned parties. And in addition to showing off their vitality and enjoying the fellowship of loved ones, they’re also reflecting on the years gone by and the decades ahead.

For some, the big birthday is all about crossing something off the bucket list. Heather Kessen and her sister, who live in Cleveland, “gifted my mom with a trip to New York City for her 60th birthday. She’s never been and we thought it would be a great way to celebrate.”

Liz Gamble of Henderson, Nev., wanted to spend her 50th jumping out of a plane, and her sister, who lives in Florida, surprised her by showing up the morning of the skydive with her best friend and a limo for the ride to the airport. “Once I stopped screaming, it was the most amazing experience,” Gamble said.

Harriette Rose Katz, a high-end New York party planner, says some boomers use milestone birthdays to relive their youth. Through her business, Gourmet Advisory Services, she’s organized blowout 50th birthday parties with 200 guests and musical acts like the 1980s rock band Foreigner. “They can get pretty rowdy,” said Katz.

Those turning 60 often find themselves honored by loved ones with a surprise party. Reggie Ishman was tricked into thinking he’d be celebrating his 60th with his wife, Sybil, in Charleston, S.C. Instead, he ended up on a flight to St. Lucia where a niece and her husband, wearing disguises, were seated one row ahead. More relatives joined them on the island, where activities included parasails and zip lines.