I'm pretty sure he was autistic. I'll try to list the stuff here that makes me think he was on the spectrum, but I may not remember everything at this moment. So I'll add more later if something else comes to me that I forgot.
1. He had difficulty making friends as a child, and was always made fun of and left out. He was apparently very quiet. He ended up dropping out of school at age 10 to pursue music fully.
2. He never took any notice of his appearance, and was always filthy. Apparently he would never change his clothes, and would put on the same clothes until someone secretly replaced them with something new, which he would put on the next morning, seemingly not even noticing the change.
3. Routine. Every night he would go to bed at precisely 10:00, and wake up the next morning before everyone else. Then he would count out exactly 60 beans of coffee (he would stand there counting them one by one). There's more but I forget.
4. He had certain rituals. Before composing, he would always dump a bucket of water over his head. Eventually the water started to leave a hole in the floor of his apartment.
5. He had horrible handwriting.
5. He was very extremely clumsy, and would knock over or break anything he touched. Literally.
6. He had an usually large head.
7. He was emotionally immature, and screamed at everyone. Very scary to be around. I'm bad at describing, but you should watch "the genius of Beethoven" to get a sense of how extreme this was (it's on youtube).
8. When you talked to him, apparently he would go on and on on a subject and you couldn't get a word in.
9. was unable to take care of himself. Near the end of his life, especially, he needed others for the most simple things, even to make him take baths.
10. Horrible manners. Here is one such example (there are lots):
"Goethe positioned himself in front of the Empress and as she passed executed a deep bow. Beethoven pushed his top hat firmly on the back of his head, crossed his arms and strode past the Empress, intentionally snubbing her. Goethe was appalled, and their friendship was irretrievably damaged."
11. One day he was walking through the woods near his house, and eventually got lost and came upon another town. He then started peering through everyone's windows to get a sense of the architecture or something so he could know where he was. He was arrested because of complaints of a "homeless man" peering through windows.
12. Horrible stomach problems his whole life (the eventual cause of his death). Maybe the reason for his deafness too. His favorite food was pasta with a cheese sauce (basically mac and cheese I guess).
Sorry If this is boring to you, I obviously have an obsession over Beethoven. Just thought it was interesting though. I know there's more... but I can't think right now so maybe I'll remember some another time.