And while we are talking bragging rights, in the early 1880s folk were doing 170 -185 miles in a day on penny farthings on roads we'd consider as mtb territory. All on skinny, really skinny, solid tyres.
But a 100 mile ride is a good thing to do, it's largely psychological, and it's a good barrier to break.
But you will quickly find all the little misadjustments on your bike, and probably make the discovery that you can talk to your arse - "Shuddup! there's only 5 miles to go, and I don't care if you're on fire".
You'll also discover that no matter how long the ride the last mile is the hardest.
Edit: don't worry, I don't think anyone took you seriously about bragging. Enjoy the ride.