You might succumb to your heart condition tomorrow. Or you might not. We can only speculate about what happens to you if you do succumb tomorrow. So the better question is what happens if you don't succumb tomorrow? And what happens if you don't the day after that? And the day after that? And the week after that? And the month after that? And year after that? And the decade after that?
Like said earlier, you might get hit by a bus tomorrow. Or you might not. And this is the exact same boat every single one of us is in.
When I was in my late 20's I decided that I wanted to learn to fly airplanes. But it was prohibitively expensive to I decided to do the responsible thing and put off pursuing that hobby until later in life when I was more settled and had more discretionary income. I figured that when I got to my 50's I'd likely be better able to afford such and indulgent hobby.
Then people I knew who were younger than me started dying through absolutely no fault of their own. Lose a couple friends like that and you soon realize that despite your best efforts, you might never live to see 50 so you'd better do the good stuff now. I took out a loan, started taking lessons and 3 months later I was a licensed pilot. A couple years after that, I was flying for a living and having the time of my life.
So the reason that you're afraid to start is the exact same reason I choose to take action. Because none of us know when the clock will run out, so better do the good stuff now.
But again in your case I think your reasons for wanting to write (achieving fame) are only setting yourself up for failure and so I would recommend you not bother. If you said that you wanted to write simply for the shear joy of writing and if fame comes out of that all the better, then I would have a different answer. But your sole goal seems to be fame. If that's your goal I'd say don't bother.
And to be fair, if I were talking to a young Dave Grohl and he asked if he should get into music because he goal was to get famous, I'd tell him the exact same thing, stay out of it because you'll likely fail. But if you were talk to Dave Grohl today, I'm pretty sure he'd tell you the reason he went into music was because he wanted to play music and he didn't care nor expect to ever achieve any kind of fame. For him, creating music for his own enjoyment was success enough. Everything that came after that was just bonus.
But that's not you. If I'm reading correctly, you only want to do it as a means to get famous and if you don't get famous, you'll likely be disappointed potentially for all of eternity. So I say you're better off not trying. Sorry to be bearer of bad news but I just don't see it being in the cards for you.