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It seems like only yesterday that "When I'm 64? became a reality for Sir Paul McCartney, but today, he hits an even bigger milestone: turning 70.

Of course, the Beatles legend hardly looks or acts his age, since he continues to remain a vibrant force as both a touring and recording artist. In the last year alone he's gotten married; collaborated on his first ballet, "Ocean's Kingdom;" performed in North America, Abu Dhabi, Europe, South America and Mexico; released a new album of standard tunes, "Kisses on the Bottom;" was honored with the 2012 MusiCares Person of the Year award; received a star on the Hollywood Walk of Fame; directed his first music video; and played at Queen Elizabeth II's Diamond Jubilee concert.

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If that's not enough, Sir Paul has plenty of upcoming plans in store for fans, including a performance at the opening ceremony of the Summer Olympics in London next month, a brand-new album that's expected out in early 2013; and, of course, more touring.

All this activity would be impressive for a rock star at any age, much less one supposedly in the twilight of his career - and that's not even mentioning all of his previous achievements, which would take several days. Let's just say that McCartney's work with The Beatles, Wings and as a solo artist has made him the wealthiest, and arguably most famous, musician on the planet.

While Macca himself has said his birthday plans will be low-key, that hasn't stopped his well-known fans from offering their birthday wishes and marveling at his remarkable career:

Aerosmith's Steven Tyler, whose band covered The Beatles' "Come Together" for the 1978 movie Sgt. Pepper's Lonely Hearts Club Band and who serenaded McCartney during the 2010 Kennedy Center Honors event, says his fellow rock legend really knows how to live life to its fullest. "He's got a whole second wind and a new childhood and a new marriage," Tyler told ABC News Radio. "Y'know, he's gettin' it every night on stage and hopefully in bed with his new wife! God bless him."

Phil Collins said he still can't believe that as a kid, he was recruited to be an extra in The Beatles film A Hard Day's Night, and now, today, he and Paul are friends and colleagues. "Suddenly, 30, 40 years later, you're playing with the guy and he knows your name and comes up and talks to you," an incredulous Collins told ABC News Radio. "It's a little bit out of The Twilight Zone." And Phil, who's basically quit making new music, says McCartney makes him feel a bit guilty about that. "Every time I say that I've stopped, I think, 'Well, he still going!'" he admitted. "I admire him for keeping going. So, happy birthday, Paul."

The Beatles and The Beach Boys have always had a special relationship, and Brian Wilson, who turns 70 himself on Wednesday, has nothing but good wishes for his old pal. Currently out on tour with the reunited Beach Boys, Wilson told ABC News Radio, "I hope he's as happy as we are, and I wish him very much luck on his concerts."

Eagles bass player Timothy B. Schmit told ABC News Radio that he wishes Paul "70 more years," adding, "I learned how to sing from listening to him…His bass playing is so unique and powerful. I learned a lot from him."

Donovan, whose friendship with Paul and the rest of the Fab Four dates back to the mid '60s, has a musical wish for McCartney. "They say it's your birthday /Buh-duh-duh-duh-duh-duh /It's my birthday too, yeah," the folk-rock great sang, delivering the opening lines to the classic 1968 Beatles tune "Birthday." He then added, "Well, I'm not 70 yet, but what I say is seven is a good number."

Randy Bachman, of Guess Who and Bachman-Turner Overdrive fame, offered up some glowing praise for McCartney's old band, saying, "As time goes by, anyone who wasn't a Beatle fan, if you don't become one now or tomorrow, you're missing out on one of the greatest pleasures of life."

Bonnie Raitt is another fan who admires Paul for "keeping going." "He is just non-stoppable," she told ABC News Radio, recalling one of his concerts a few years ago where he blew her away by performing for three hours and playing an amazing guitar solo on a rendition of Jimi Hendrix's "Foxy Lady." "I couldn't even believe it was him on guitar," she said. "He is really showin' us how to do it…He's just one of our greatest songwriters ever and such a great singer and a great person. He's just… not a jerk!"

Squeeze's songwriting team of Glenn Tilbrook and Chris Difford were sometimes compared to McCartney and Lennon during their own band's heyday. Tilbrook told to ABC News Radio about Paul, "There's not a time when I hear a Beatles record and don't gravitate towards what he's playing on the bass…If he did nothing else, his bass playing is amazing. I wish him all the very best." Difford added, "'Listen to What the Man Said' - that's the first song that springs to mind. I think he's an incredible artist."

And lastly, Faces/Small Faces keyboardist Ian McLagan, whose bands this year joined McCartney and The Beatles in the Rock and Roll Hall of Fame, said, "Happy Birthday, Paul. God bless ya. He never stops. God, he's amazing."