…who died either before you were born, or when you were still a child?
And much later, after coming of age, you saw pictures of them and heard their voice and were mesmerized? And felt weird for having a crush on a dead celebrity (who was über-hot when he/she was alive)?
Because, that’s exactly what happened to me quite recently.
Audrey Hepburn died when I was 11, so I think she fits, but I don’t feel weird at all for acknowledging that she was one of the most beautiful celebrities I’ve ever seen.
This doesn’t quite qualify, but…Katharine Hepburn.
She was 58 the year I was born, and died when I was 38. And, even as an olde woman, she was striking. But, when I was an adult, and saw pictures and films of her when she was young…WOW.
Audrey Hepburn for me too. I was about 10 I think and it was My Fair Lady. This was in the early '80s. I still have a crush on her and do not feel weird about it.
I wonder if there’s a name for that condition?
For me - I’ve mentioned it before - it’s Luke Kelly. Yes, the Ginger Dubliner to end all Ginger Dubliners. He died of a goddamn brain tumor exactly 4 months and 8 days after I was born.
No, he certainly didn’t have a “classic male beauty” or “pretty boy” face, but I find him strangely handsome. And don’t get me started on his voice, charisma and integrity. (Holy shit, that VOICE!)
Yes, I’m a bit crazy about Luke - but as he said once, my head’s only woolly on the outside! 
Greta Garbo. I had to watch Camille twice: once to moon over Garbo, once to figure out what was going on.
Peter Tosh for me. I actually ached to know he was dead and I never got a chance to see him in concert and feel his magic in the same room as me.
Audrey Hepburn is interesting. I know a lot of men who had a crush on her. My husband told me that when he was a very small child, he was fascinated with Breakfast at Tiffany’s, and he thought she was amazingly beautiful and he liked her. Later, he said, he couldn’t for the life of him remember what he thought was so attractive about her. He said she simply wasn’t the slightest bit attractive to him anymore, but he remembers that she was the prettiest thing ever when he was young and watching those movies.
Ornella Mutti (pre-Flash Gordon) and Diane Lane (Streets of Fire).
Marvelous.
One more vote for Audrey Hepburn.
I’ll go with Francis Farmer.
Barbara Stanwyk. Ye gods,
Rita Hayworth.
There is a popular animated gif I’ve seen here and there and I watch it over and over every time. I don’t know what movie it’s from. She tosses her hair and turns toward the camera…holy shit that was a good-looking woman.
I think that’s her entrance in GILDA, made quite famous by its inclusion in THE SHAWSHANK REDEMPTION, which you should run out and see.
Gregory Peck is my platonic ideal of manhood. Please note that’s platonic idealism, and not platonic love, because I would give my eyeteeth to be able to go back in time and do unspeakably sweet and filthy things to that man. 
He didn’t die until I was 22, but given that he was 55 when I was born, I think it’s close enough.
Neither of these two fit the criteria of the OP.
He died in my late teens, I beleive, but I had a total obsession for James Cagney in my teens.
I blame Yankee Doodle Dandy.
Elvis
Every time I watch Casablanca I marvel over how beautiful Ingrid Bergman was.
Along these lines, I’ve still got a bit of a thing for Donna Reed circa “It’s a Wonderful Life”. The movie itself was 31 years old when I was born.
Oh, honey, Ronald Colman.
Gary Cooper.
And I’ll fight **Shirley **for Jimmy Cagney.
James Mason.