When I first started "telling" stories to myself as a pre-teen, without writing them down, I set almost all of them in a fantasy landscape that was essentially an expanded version of the farm where I was growing up. For example, we had 7 ponds on our land, and so my fantasy world had 7 seas. Real world creeks became fantasy rivers, and small groves of trees became forests. Even today, some of my fantasy stories take place in a variation on that original world building.
I also know that Robert E. Howard, among other writers, did much the same thing when he began writing. A lot of his stories use the Texas landscape where he lived as the background, although it certainly isn't called "Texas" and quite often some green-walled ruin will rear out of the harsh landscape.
Is this actually a common practice among writers? Is this how everyone gets started? This seems like a potential essay idea but I'm just in the beginning thinking stages about it. Maybe some of the folks in the fantasy world called "blogosphere" might have input?