Comedian Billy Crystal has weighed in on why women and men can’t be friends (according to his character Harry Burns in “When Harry Met Sally” the “sex part always gets in the way”). Now he's reportedly writing a book offering a male perspective on aging.

The 64-year-old is said to be working on a book on “senior citizenship, which sources say is hilarious,” according to the Hollywood Reporter. As the Reporter noted, Billy Crystal has been talking about aging for…well…ages. (“[In your sixties] you’ll have a major surgery, the music is still too loud, but it doesn’t matter because you can’t hear it anyway!” he groused to a group of middle schoolers in 1991’s “City Slickers.”) And in 2009, he dusted off his one-man Tony-Award winning biographical show “700 Sundays” -- which takes viewers on a journey to the characters who’ve made up his life from his youth to adulthood -- for a limited run.

It seems like 2012 may just be Crystal’s comeback year. He’ll make his return to the big screen on Christmas Day alongside Bette Midler in “Parental Guidance,” in which he and Midler play unsuspecting grandparents babysitting three rambunctious grandchildren.

The new movie reportedly took five years to get made. When asked in an USA Today interview what took him so long to return to movies, Crystal responded,"It wasn't planned. I wasn't getting offered any scripts I liked."

December's "Parental Guidance" marks his first big studio movie since 2002’s “Analyze That,” a sequel to “Analyze This” where he played therapist to Robert De Niro’s unhinged mob boss. Crystal stayed busy in the interim however, voicing the walking eyeball Mike Wazowski in “Monsters, Inc.,” a role he’s called “his favorite character ever.” He’ll reprise the role in 2013 for the sequel “Monsters University.” He also appeared in an indie comedy called “Small Apartments” that screened at South By Southwest this year.

Check out the slideshow below for some of Billy Crystal's best performances and funniest moments over the years.

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  • Billy Crystal

    Billy Crystal on the red carpet in 2012.

  • EXPLICIT LANGUAGE: 'Analyze This'

    Billy Crystal plays the psychiatrist of a mob boss played by Robert De Niro in the 1999 film "Analyze This."

  • 'Throw Momma From The Train'

    Crystal stars in the 1987 film "Throw Momma From The Train" directed by Danny DeVito.

  • 'City Slickers'

    <em>"Fifties you have a minor surgery. You'll call it a procedure, but it's a surgery."</em> In this scene from the 1991 midlife-crisis film "City Slickers," Crystal lectures a classroom of children about life.

  • 'When Harry Met Sally: 2' (NSFW)

    Finally! The sequel for "When Harry Met Sally"... without Sally. (Not suitable for work -- or for those with a disdain of sophomoric humor.)

  • 'Billy Boxer'

    Billy Crystal discusses boxing as former boxer Tony Minetti on "Saturday Night Live."

  • 'Sammy And Ronald Reagan'

    Crystal performs in a skit on "Saturday Night Live" as Sammy Davis Jr.

  • Bowling Alley

    Everything is "unbelievable" for Crystal in this skit where he plays a bowler.

  • 'Winston University'

    Crystal plays a college recruiter with an unlikely plan in this "Saturday Night Live" skit.

  • 'Saturday Night News Segment -- Weather Report'

    Crystal delivers a scathing weather report as weatherman Lew Goldman in this "Saturday Night Live" skit.

  • 84th Academy Awards

    Billy Crystal performs during the 84th Academy Awards in 2012.

  • Billy Crystal

    Billy Crystal arrives at Muhammad Ali's Celebrity Fight Night XVIII in 2012.