It's not about age, rather desire and determination. A negative side of age on cleaning up is that the individual has this an excuse, "I'm too old to change." You can let your friend that someone is never too old to better their life and that life isn't over till we are dead. In the end, its not about love; don't allow yourself to be an enabler. Your friend's choices are their's and you can't allow yourself to make them or their habit your problem; it will decrease the quality of your life and you will be yet another one lost to the negative affects of drugs and alcohol. Good luck!
I am assuming you don't have trouble. If you are very close to your friend it can be difficult to remain objective. No one can defeat a habit until they admit they have one. Even then they need someone who is neutral that they can trust to help them through the difficult part. Nothing worthwhile comes easy. There are several agencies that provide the mentors and discipline to carry them through. Good luck.
Lifesaver is right. Ur friend has to want it and be willing to make changes. A good support system helps and also agencies. Unfortunately many ppl go in and out of rehab many times before making the change. Remain supportive and set limits with it friend. Hopefully she's motivated to make the change.
If the person doing the drugs doesn't THINK they have a problem, or doesn't realize all the NEGATIVE effects that their drug use has had on their LIFE, then they will almost guaranteed NEVER stop until they die. Addicts wear blinders. For the most part they don't really care about much else other than using, BUT as long as they can/are using, then they can continue to float along through life dodging anything IMPORTANT or REAL. Everyone has their own personal rock bottom, for some the bottom is death, for others it's when they finally have that one last thing happen to them that brings their use to the forefront and they are forced to see it for what it is. The best thing you can do is talk to the person and express your deep concern for the person, OR, get an Intervention set up. Good luck to you and your friend. I'm always willing to talk about this, so keep that in mind.