Jack Nicholson and Michael Keaton are 14 years apart. Remember that Gabrielle Carteris was 21 when she first started filming Beverly Hills 90210, when she was supposed to be 17-ish in age for the role. Assuming Joker was in his early 20's when he killed Bruce's parents, and Bruce was roughly 8, you're talking about maybe a 5 year difference in Nicholson's actual age vs the age he portrayed Joker to be? Definitely plausible.

So, to answer the question, Batman would be mid-to-late 40's and Joker would be about 60. That's pretty much what it looked like on screen.

Jack Nicholson and Michael Keaton are 14 years apart. Remember that Gabrielle Carteris was 21 when she first started filming Beverly Hills 90210, when she was supposed to be 17-ish in age for the role. Assuming Joker was in his early 20's when he killed Bruce's parents, and Bruce was roughly 8, you're talking about maybe a 5 year difference in Nicholson's actual age vs the age he portrayed Joker to be? Definitely plausible.

So, to answer the question, Batman would be mid-to-late 30's and Joker would be about 50. That's pretty much what it looked like on screen.