They look no different from the first movie. Only difference is they're carrying a kid around with them. They look much too young to have kids. They should look like adults which they don't to me lol.
Mavis is a vampire and therefor not really aging unless she chooses to look old (If you go by original Dracula lore). In general though this film has very stylized animation. If not for the long chin Dracula looks to be her age and the Frankenstein Monster, in another outfit, could probably past for a monster high foot ball player.
Well Johnny's hair was a little shorter, and his face got a little rounder, so he did change a little. He's only in is 20s remember. I'm surprised neither Drac or Mavis turned him though. Unless they do, he's only going to be with them for about 60-70 years. I'm thinking they'll change him at some point down the line. Hey, maybe that could be the plot for the 3rd movie if they make one, Drac trying to sneakily turn Johnny.