If you're still on the fence, write the damn book. Given the choice, why not err on the side of action?
Don't take the chance and you'll go on wondering what would happen if you did. Deciding to write, to seriously write, is a momentous commitment Especially when you're older. But not deciding, that's worse. Postponement is true punishment.
These aren't the only two options, of course. If there's anything you'd rather do with your life, sing or speak or start a company, go do that. Just don't not decide to write. Doesn't the fact that you consider yourself on the fence mean that it's time to get to work?
One of my favorite scenes in Being John Malkovich:
John Malkovich: From now on, I'm no longer an actor. I'm a puppeteer.
Agent: OK, Great.
John Malkovich: And I would like to redirect my career so that from now on, the name John Malkovich will be synonymous with puppets.
Agent: Sure, no problemo. Poof, you're a puppeteer. Just let me make a couple calls.
Clearly, not the first time a client has walked in the door with a major change of creative direction. No point in fighting it.
Have the courage to be your own talent rep: "Poof, you're an author."
It doesn't matter how successful you are at whatever it is you currently do. Just because somebody has a dream job doesn't mean it's their dream job. Any actor would kill for Jim Carrey's career, but Carrey prefers painting to comedy. Michael Jordan switched to pro baseball at the peak of his basketball career. The great Gene Hackman hasn't made a movie in almost twenty years—but he's written or co-written five novels.
Be bold. What will a minor tweak accomplish? "Maybe I'll take a writing class. Or start a blog for friends and family." Calibrating your current situation a few degrees won't tell you whether you've been driving down the wrong road all your life. You're still a veterinarian even if you start specializing in calico cats.
To know where you really stand, pull the rug out from under yourself.
By taking up the pen, you may veer into everything you've ever wanted. Or, like Michael Jordan, you may find yourself veering right back to where you began. If you do, however, you return with the confidence that you're back where you belong.
Don't leave the question unanswered. Take that sabbatical, live off your savings, do whatever you can for a few dedicated months. Embark on Campbell's heroic quest. Leave the comfort of the known behind and enter the wild and dangerous world.
Returning after many trials, you will have a hard-won elixir to share with the tribe. In this case, a finished book. And that may be enough. Like Samwise Gamgee, you may return from the Mordor of the writing process convinced you never have to leave the Shire again. Writing a book is a great deal of effort and sacrifice for a single life lesson, but could you learn a more valuable one?
There is no greater comfort than the conviction that you've found your place in life—even if that place was your point of departure.