Is it okay that I want to befriend a mentally challenged person?
Why do you want to befriend them?
I have never had a mentally challenged friend before and they seem nice.
It's good to befriend others. However, you need to make sure you aren't just doing it for selfish reasons.
My motives are pure. I'm sure being friends with them will be good for both of us.
You're right, I'm sure you'll both benefit if you become friends. It's important that both people are having fun in the friendship, not just one person.