Recently I've been reading "The Plot Thickens" by Noah Lukeman. It's taking me awhile because I'm studying and taking notes, but even though I'm only on page 100, I'm amazed by the value of his book. The first two chapters are about getting to know your characters, inside and out. In those chapters, Lukeman has created enormous lists of questions which help a writer develop an incredibly detailed bio of her characters. The result is that by the time you finally write your story, it practically writes itself because you have come to know your characters so deeply. An added advantage is that characters written from such a detailed background come across as three dimensional and real to the reader rather than flat and stereotypical.
So I might not be a cagey old grandpa or a spunky twelve-year-old super-spy, but thanks to Noah Lukeman's help in fully developing my characters, I can get into their heads and be them and even have their adventures for awhile. And the better I'm able to live through my characters, the better my readers will be able to do it, too. So the moral of this post is that in real life, yes, you do want to be yourself, but when it comes to writing, you don't have to be. When you write a story, you can and should be someone else sometimes, at least temporarily.