And you must be attracted to them in their current state, no fair saying “so-and-so, but back when she was in her prime!”
Whose old bones would you jump right now?
Faith Hill
ETA: She’s 42. Please, no debates on whether she is “old”. My answer fits the OP’s question. 
Helen Mirren
Sean Connery
Fits perfectly, thank you! And thanks for posting her age, I should have suggested that.
Robert Duvall, in a heart beat. Especially if he wore a cowboy hat and talked like Gus McCrae. I’d do Tom Hagan too, if I had to ;).
Turned 79 yesterday, I think.
Emma Thompson, 50.
I want Gene Wilder, age 76. And if he’s not in the mood, Harvey Keitel, age 70.
Leonard Nimoy is still smoking hot to me. He’ll be 79 in March.
Fran Drescher, 53
Tilda Swinton, 50
Lisa Kudrow, 46, beats out Sandra Bullock (45) and Kristin Chenoweth (41) on age. I’d tumble any of 'em. 
Tony Bennett (83)
The man’s an octogenerian and still smokin’!
Susan Surrandon’s still hot, at 63. I’d hit it.
For some reason, I’m having a harder time with men. I have an inexplicable crush on Deforest kelly, up until about Star Trek II (after which he becomes a cute old man who I don’t want to sleep with - no, I don’t get it either), but as he’s dead now, I’m not sure that he fits the OPs criteria. But if he does, I believe he was 62 at the time.
David Bowie (60), Robert Downey Jr (44), and Christopher Walken (66, I think).
seconded - he just keeps getting better with age!
Jane Goodall. Seriously, I thought she was really cute when she was young and I thinks she’s still attractive.
I was gonna say Tilda Swinton, she’s hot. I met her in person and she’s hot. Though Susan Sarandon is older, so I might have to go with Susan Sarandon. After Susan Sarandon I’ll put down Sigourney Weaver.
Jane Seymour, 58
Olivia Newton-John, 61
Susan Sarandon, 63
Helen Mirren, 64
Catherine Deneuve, 66
Faye Dunaway, 68
And the winner is:
Raquel Welch, 69
Maggie Cheung, 45. There may be someone older, but I’m drawing a blank right now.
Madonna, 51.