How to handle my brother's forgetfulness?

tl;dr: brothers forgetful behavior has been escalating to the point he left a stove burning today. I'm scared he'll start a fire, how do I approach him about this without seeming like I'm attacking him?

Making a throwaway because I'm pretty sure he knows my main. I'm going to start out by saying my (26) brother (25) and I are both different levels of ADHD/Autism. I understand part of the issue is this for him, heck I forget stuff sometimes as well. But I also feel that part of it is the fact he got so used to our mother doing everything for him while we were growing up since his symptoms were so much more outwardly apparent.

He constantly forgets his dirty dishes and garbage/containers out on the table and counters. He'll leave the garbage can overflowing to the point the drawer its in won't shut and stuff gets stuck behind the can and insist he was going to take it out eventually. He'll say he's going to feed our cats and then I have all four of them swarming me because it's been a couple hours and he never got around to it. Or if he does feed them, he just leaves the dirty cans and lids out on the counter and the old bowls that the previous food was in out on the floor and crusted over.

What's really scared me at this point though and why I'm making a post is the fact that I walked into the kitchen after he made himself lunch this afternoon because I was smelling gas, and he'd left the stove burner on full blast. Not an electric burner where I'd maybe see if it just glowed and he hadn't noticed, a full, open, propane flame. He's done this before with forgetting to shut our oven off as well.

I'm scared that if this had happened while I was gone, he could have started a fire, our cats also (although they aren't supposed to) have a habit of jumping on the counter/stove. One of them could have gotten burned.

I just don't know what to do. Every time I try to bring this up to him, and express the fact that I'm worried he's constantly forgetting to do things, and that I'm frustrated that I'm constantly left picking up after him, he just completely shuts down. He acts like I'm attacking him no matter how calmly I approach him and I'm really at the end of my rope here.

The cleaning is annoying sure but not dangerous, but I'm scared now that he could forget to shut the stove off again and cause a fire. Is there any way to approach this differently without having to sit and watch him every hour of the day???