Well, i'm 21 with aspergers and dyspraxia. After many year of disecting jokes and even reading every joke in one of those 100 joke books i managed to work out why some things are funny, but not all of them and i don't always laugh. I have however developed my own sense of humour that relies mostly on irony. Watching the latest batman movie, i found scaringly enough the joker's sense of humour was close to mine. I laughed on the scene where he had set the truck on fire, because he had chosen to set a firetruck on fire rather than an ordinary one.
Dunno, just my sort of humor. Like the film 'mirror mask' that is a text book definition of my sort of humor.
I also find myself laughing when people go through predictable patterns of conversation. Like 'hows the weather' etc, its like a check list they go through - find it hard not to laugh when i make a comment about the weather or family or something.
From my point of view, i think sarcasm may cause more problems than jokes. I still find it difficult at times picking up sarcasm.