Once I regained my memories from before my exile, I suspected that my inability to astral project or connect to the astral plane (outside of a general sense for beings in my vicinity, if powerful enough) would also affect my ability to die (If I can't leave my body temporarily, there's no way I'd be allowed to leave it permanently).
I had walked away from two 50+mph impacts (one car hit me while on a bicycle, one car hit me while on my motorcycle, never getting more than bruised), I'd also pretty much never gotten sick outside of a yearly cold (when the temperature changes dramatically)
Also took large amounts of painkillers for migraines (due to light and sound sensitivity, I have to wear sunglasses pretty much 24/7 outside of my home, especially with LED lighting), One of which should have destroyed my stomach or liver years ago, I've never had any side effects.
Now all this being improbable but not conclusive, and partly due to very much wanting to go home, I bought two bottles of pure helium and set up a bubble. Set myself up high enough under the bubble for any oxygen to sinc below me, then emptied the first bottle. During the first 15 minutes it appeared to be working, until I snapped back to normal and never felt anything since (The only "side effect" I felt was after leaving the bubble, an hour and 15 minutes later, when I started breathing air again. Massive headache for a couple of minutes).
Just in case, busted out the second bottle, aimed right at my face this time, and tried again. another hour and 15 minutes (ish) later, not a thing..
Long after the bottes were empty and I still sounded like a chipmunk. And since then, I can't get drunk anymore. Which sucks.
So yea I think immortality is possible (Aging I'm still fuzzy on. I'm 40 but I almost never get taken for anything over 30-32. But that could be the millennial thing I've heard about)