If there's any comic book character that Dicaprio or Daniel Day Lewis (if he comes out of retirement) would play, at this point it's safe to say it's probably Joker.
I have no issue with a Joker that's significantly older than Batman because Joker for the most part isn't meant to be a physical threat to Batman and it's very easy to write him in a way in which he isn't going toe to toe with him but is still dangerous. He uses chemical weapons, schemes, henchmen, etc. That's usually how it is in most stories.
I'm pretty sure there are mob bosses, terrorists and criminals that are 70 years old. Heck, the deadliest person in the world, the US president, is almost 80.