I'm 27 and female (you should know this by now, hehe).
I'm not too restrictive about what I consider friendship. I have "this stage of life" friends and "always friends".
My husband is my best friend, and satisfies pretty much all my human interaction needs when he's home. Haha. Seriously, when I have a choice of doing something with him or someone else, I'd always rather do things with him. He knows me better than anyone else in the world. Although my parents come in a very close second.
Another blogger here, LobsterHunter, is a real life friend. We were childhood best friends, and though we have grown apart with time as far as life circumstances go, she's still very much a friend. She was the Maid of Honor at my wedding, and even came to stay with me for a couple of weeks when my husband was deployed. She's an "always" friend. We could go a year without talking and still pick things right back up. I put my friend Chris in the same category. We haven't talked in quite a while, but we could pick things right back up where we left off.
Here in Hawaii, I have "this stage of life friends"...we talk and cry (and throw dishes, lol) together, but when we move, the friendship will dissolve or fade or whatever. That doesn't bother me. When Lani calls me in the middle of the night upset and asks me to go meet her outside, I will. She's done similar things for me as well.
I'm not one to have day-to-day, let's go do everything together friends. My husband is all I need when it comes to that. It's more of being there when a friend needs me, and vice versa. We each have our lives and our families and our own things going on. When there's a need that the other can fill, we seek each other out, whether it's everyday for a week or once every other week.
I think online friendships can be friendships just as much as real life ones. Not all online friendships are the solid, I care about you kind...more of the...we have stuff in common or I find you interesting, let's chat every-so-often kind.
I have some friends online that have been every bit as much of a friend to me as any real life friends. My friendship needs are usually not physical ("Can I get a ride to the airport?"), but more emotional needs. Because of that, some online friendships can be just as solid and real to me as any others.
The "always" friendships are more rare than the "this stage of life" friendships, but I treasure each. I appreciate anyone who is willing to care for me. I don't mourn the loss of "this stage of life" friends, either, nor does it make me feel bitter or that they weren't really friends. There was something we both needed during our friendship, and we helped each other with that, and when it was over, it was just natural that it was over and we grew apart. That's ok.