I’m 23, for the record.
Joey Heatherton - 65 - for those who remember the Serta Mattress commercials. I didn’t know what a Serta was when I was a kid but I know I wanted one desperately.
Add Al Pacino and David Bowie to my list too. And of course everyone knows I’d give my left arm to do Alice. 
I’m 42.
I’m 39, but ever since I first saw Willy Wonka and the Chocolate Factory, I wanted Gene Wilder more than all the candy in the world. 
I’ll take (now both Sirs) Patrick Stewart and Ian McKellan, with a side of Leonard Nimoy . . .
Raquel Welch is my answer… she’s been my fantasy cougar for most of my life. She’s now what, 69? She’s still smokin’!
I’m choosing to answer this by picking the oldest celebrity I actively lust after, as opposed to celebrity I would do. Michelle Pfeiffer is still hot – smokin’ hot for her age – but I don’t really get revved up for her.
Marissa Tomei, at 45, OTOH, I drool over.
I’m 39. Yeah, yeah, a guy who isn’t really into older women. Big surprise.
Oh, Leonard Nimoy! Absolutely able to live long and prosper in my pants, at age 78.
That was the age difference between my first girlfriend and myself (I was 18, she was 32). My folks were not happy.
Dana Delaney is in her mid-50’s and still smokin’.
I actually forgot the oldest one on my list:
Nigella Lawson, 50.
She doesn’t even have to cook, although I certainly wouldn’t object.
Seconded, along with a lot already listed. To step it up a few decades, I nominate Sally Kellerman at 72. Still looking like Hotlips, and her shower scene in MASH is tattooed in my brain.
Salma Hayek (44)
Seconding Timothy Dalton – they just don’t make men like that any more.
He’s 63 and I’m 44.
Does it count if they’d be pushing 70 now if they were alive - but unfortunately they died at 43?
Agreed. She was the MILFiest MILF I ever did see in Step Brothers. Really attractive. And not Botoxed up at all, like it seems now.
In person, and up-close, she looks even better. My chorus performed with her a couple of years ago, just after she turned 60. Up-close, you can tell she’s had work done (no 60-year-old looks ***that ***great), but it was done very subtly. They softened her “smile lines” without removing them.
And yes, she’s as nice in person as you’d think. If I were straight, she’d be at the top of my list.
Well, if that counts, I’ll have to add George Harrison, Frank Zappa and Leslie Howard.
The oldest on my list was Derek Jacobi - 71. I’m 47.
I’d second The Daltonator, but I think I’m too old for him.