What may my friends disease be?

My friend told me as a secret that he has 10 years left to live. He is now 26 years old. Until now he was extremely involved in good nutrition and healthy life. He always wanted to be with happy and positive people. He is pretending as a happy person always and hates depressive people, stays away from them. I was shocked when i heard this from him. He recently told me he has only 10 years left(even his family doesn't know the fact). He never tells what it is. If this started some years ago, do you know any disease causes death in 10 years? Any opinions?