I started trail running right when covid started because of where I live (Gatineau park) and because I was always a slow road runner... you forget speed in trail it's more about being smart of psychology and how you handle the pain.
I went from 227 to 193-94 the past year so I am still a heavy runner. I ran my first 50k in august of this year and I was completely destroyed after because I focused on running only for a year, never did any weight training etc. I found muscle, tendons etc that I never knew I had in those mountains lol.
I got a ''préparateur physique'' that is also an ultra trail runner and I spend at least 3-4h a week just on my legs now. My goal is to drop down to around 180 before the race next september (100k).
Really enjoy the challenge but it's really of mix of running / nature / survival / being smart. At some point you know your body and learn when to run, hike/ walk etc.
Only professional runners or really good athlete will run the entire distance, it's rough, there's something called shuffling in running (youtube) or power hiking in this case that you need to master before those long races.
For your age, I see runners from that ''age'' in every race i've been too so it's not too old
Here's a good doc on youtube about a 100 miler father daughter moment: