Well, chrisrolinski, I guess you have no reasons to drop. In your case, I guess you are happy with what you do so it is not that you have given much but that you truly like your PhD.
And yes, I have the idea that years go very fast and suddenly your twenties are all gone. However, I believe it all comes down to whether you like your PhD or not. If you don't, you are certainly wasting your youth, right?