If you think you have a problem, try quitting. You can do it.
I'm 27 and also about to start a grad program this fall actually. I'm afraid of ruining everything I've worked towards too. I'm on my 9th day sober, so pretty early on. However, I did have a good stretch of 9 months sober that ended last year. It did feel great and I got a lot accomplished for working towards getting into a grad program.
I promise it feels so good knowing that I was always with a clear head and was able to put my best efforts into everything. I promise it's worth it!
:-)