The Rambam in Hilchot Teshuva talks about what a true Baal Teshuva is. He describes this as someone who stumbles by sinning, and he sincerely regrets his indiscretion. He becomes a true Baal Teshuva when confronted with the same sin, but this time refrains.
The Rambam also refers to a strange Gemara in מסכת שבת that talks about different physical signs of aging that ultimately ends with a person's death. There are signs of such aging in one's forehead and in his eyes. It also can be seen in one's jaw that all show deterioration.
While all of this is painfully morbid, the Rambam does this in order to make a point. As long as there is still a breath of life in an individual, as long as he acknowledges Hashem as the Creator, and he shows genuine remorse for his sins, he will be saved and granted a share in the next world.
We must never despair. There is always room for Teshuva!