I'm sure I've seen clients with Asperger's - it was only recently that it was given a name. It used to just be called "a bit odd." The character Sheldon Cooper on Big Bang Theory is (unofficially) based on Aspergers and you'll see him do a lot of typical Aspie things.
My brother is pretty much classic Asperger's - but he's 50 years old and there was nobody to diagnose it when he was growing up. What I can tell you to expect may include a sort of physical stiffness and awkwardness. They are often not cuddly people and hugging them can be a bit like hugging a coat rack. It's a bit weird but nothing alarming. Aspergers generally means they don't pick up on subtle social cues like disapproving glances, etc. so they also can do odd things that other people may consider graceless or rude, like pick their nose in public or something like that. (That's my brother!) They may talk in a monotone drone, not recognising that their audience is bored or uneasy as they go on and on about steam trains or The Who (my brother!) or whatever their particular interest is. Jokes and sarcasm may go over their heads and they will take what you say at face value.
That he has told you this about himself means that he is aware of these issues and hopes you will work with him on them. Therefor, you can probably get away with correcting any inappropriate behaviour. He may appreciate being told if he is kissing you poorly. I mean, if a guy licks my ears I will probably try to find a way to distract him before I actually tell him not to do that. I think with someone who is telling you up front that they have this issue, they may be prepared for/used to/appreciative of being told - nicely but directly - that something they are doing isn't working for you.
You may find the booking tedious and awkward but I don't think there is any particular reason to be afraid or worried.