In the book, I believe he's 36. In the musical, 37. And in the play, 40.
I seem to remember some exchange in the play in which Valentin mentions that Marta is 24-- "two years younger than me," he says. "Thirteen younger than me," Molina replies. Valentin glares at him. "Okay, sixteen."
Or something like that. It cracked me up when I read it.
"I hate musicals... People don't sing in real life."
"Well, maybe they should."
--Kiss of the Spider Woman (cut line)