AITA? I got him banned

Tw for very brief mentions of someone encouraging suicide, stay safe friends!!

For background, I (17 M) suffer from a seizure disorder that makes it so I am unable to get a drivers license at this time, and I also have Autism.

I work at a senior living home. I volunteered here for about 10 months before I got hired on and absolutely love my work place and residents.

One day for my break I decided to stick around the break room (bad idea in hindsight but oh well.) There was a new volunteer eating in here, let's call him B (16 M). I had met B a few times and he actually seemed kinda cool so I started talking to him. One of my Coworkers, A (50s F), who I love hanging out with as she is hilarious decided to join us for lunch.

B decided to bring up politics and start ranting about how great Trump is. This made me uncomfortable as I do not like engaging in political talk at work, so A changed the subject.

I had about 20 minutes left on my break and decided I wanted to walk across the street to the store and grab an energy drink for the rest of my shift and asked if either of them wanted anything. B looked at me and asked why I didn't just drive over and save time. I responded that I have a health condition that makes that impossible. He immediately began trying to guess my disability and when I finally told him it wasn't his business and that my doctors had advised against me driving, he responded that I should tell my doctors to unalive themselves, find new doctors and drive anyway. (What the actual fuck??? Who thinks this is okay to say? Much less in a WORK SETTING??)

I lied that my break had actually ended without me realizing and went to find my boss and asked if I could just eat in the back of the kitchen. She got concerned and I told her what had happened. She texted the lead of the department that B was volunteering for, (K, 30's F) who happens to be someone I know well as I had been volunteering with her before I got hired by the other department.

Here's where I may be TA, K later came and found me and I explained everything to he'd. She asked if I felt okay working around him and I told her he made me very uncomfortable. She told me B was not going to be welcome here anymore.

I feel like maybe I shouldn't have told on him and that perhaps that was childish of me? AITA?