How fast does lou gehrig's disease progress?

GORK. It is unpredictable of how fast ALS (lou gehrig disease) will end up in death. It depends on the person, its presenting symptoms, the velocity of progression, institution of treatment etc. There's only one medication approved for that by far called riluzol. In most cases, though, it progresses to significant disability in a matter of 2-3 years.
Very fast. Death can ensue within 3-5 yrs. With supportive care, patients may survive longer, but without mechanical devices, and artificial support, survival is short-term unfortunately.