In March of 2008, it was released by the National Alzheimer's Association that there are over 250,000 kids between the ages of 8-18 that are in the caregiving role to a parent/grandparent with Alzheimer's disease. This is utterly shocking!!! These kids should be out having fun with their friends, play football, being a cheerleader, not baby sitting a parent.
As they get into their young teens not only are they dealing with learning who they are, finding their own independence, dealing with hormones but dealing with a parent that is slowing dying before their very own eyes and may or may not be there to seem them graduate from high school. I know for me that is my dream is seeing my son graduate high school and this year I will be lucky in that I get to see him graduate from junior high. No one knows what the next four years will hold.
Below are some links that might help your teen understand what is going on with your loved one:
Just for Kids and Teens http://www.alz.org/living_with_alzheimers_just_for_kids_and_teens.asp
From the Mayo Clinic - Helping Kids Understand Alzheimer's