Incidence rates of ALS increase with age, peaking between 70 and 80 years. Amyotrophic lateral sclerosis is a fatal condition for most patients with mean life expectancy of about 3 years after diagnosis, although some patients live longer.
Poliomyelitis is a viral infection affecting the nervous system which causes motor neuron disease. Although it has been eradicated by vaccines developed in the 1950's, polio survivors can suffer from post-polio syndrome for several decades (mean of 36 years) with gradual weakness, fatigue and muscle wasting. A study published in 1994-1995 estimated there were about 1 million polio survivors in the U.S., with 443,000 reported having had paralytic polio. Considering 25 to 40 percent of polio survivors develop the post-polio syndrome, it is one of most prevalent motor neuron disease in the elderly population.1
Links:
[1] https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Post-Polio-Syndrome-Fact-Sheet