Can someone under the age of 20 get als?

Not typical: Average age of diagnosis is 55. Can be seen as early as the 20's most commonly between 40 and 70 years of age.

Very unlikely: However, there are hereditary disorders of the motor neuron which occur in childhood and may even present in early 20's. These disorders are somewhat similar to ALS, but clearly distinguishable. ALS tends to occur in middle age and later.

It is rare: It is rare for a youngster to be diagnosed with ALS but it is possible. Most cases of this occur after age 50 or so.