Almost all male citizens of the United States age 18 through 25 are required to register with Selective Service.
If your family member needs help, a friend or relative may help him fill out the registration form.
Men who have disabilities that would disqualify them from military service still must register. Even though he is registered, he will not automatically be called to serve in the military.
If your family member doesn't register, there is a risk of losing their benefits, like SSI or MassHealth.
When to register:
It's best to register within 1 month of his 18th birthday (1 month before or 1 month after).
After that, you can file a late registration up until his 26th birthday.
After turning 26, he is too old to register.