I have experience working with physically disabled adults, so YMMV, but I can give a few comments.
Most importantly, do you like people and does hanging out with just your client sound like fun? You don’t have to be a completely social person, but you will spend time talking. You might work closely with other assistants/care providers.
Your duties will vary according to the needs of the person you are working for - you might help with bathing, preparing food, shopping, cleaning, supervising, etc, as well as providing companionship. You might also spend a good part of your time reading or watching tv.
You’ll be doing the same sort of duties as a child care provider. If you can handle having your patience tested, and you don’t mind doing things that might be a little icky (helping with going to the toilet, for example), you’ll do fine.
The job can be physical so you would need to only work with clients who are unlikely to need physical assistance - you wouldn’t want to work with someone who likes to run away or someone who you might have to lift. In other words, you need to know your limits and stick to them.
If you’re lucky, you’ll get to meet lots of new people and you’ll grow to really care for them. It’s truly rewarding - it feels really good to make someone smile.
However, there are always situations that will be difficult - you’re working with people. Not all mentally (or physically) disabled people are sweet or nice! If you are good at dealing with difficult people, you can turn it into a better situation, but you will need to learn your limits and when you need to quit.
So, if you like to talk to people, have some patience, and have a good attitude, give it a try.