It is difficult to predict the extent to which male pattern baldness will cause hair loss. Generally, though, men who experience hair loss earlier in life will be most likely become fully bald. If you do not notice symptoms of pattern baldness until after your mid-twenties, you will likely still have hair, albeit thinner hair, when you reach old age.
It may be worth finding out the extent to which male pattern baldness has affected older men in your family, especially your maternal grandfather. Comparing their history to your own experiences may give you an indication of your eventual hair loss.