"But not someone who collects SS due to age?"

Yes, as long as they are getting their payments by Direct Deposit, then get their stimulus payment electronically; otherwise, it will be a paper check.

Are you subscribed to any of the e-newsletters:

https://public.govdelivery.com/accounts/USIRS/subscriber/new?preferences=true

You get these to your inbox, timely.

For instance:

"Payments will also be automatic for people who receive Social Security retirement, disability (SSDI), or survivor benefits or Railroad Retirement benefits who don’t normally file a tax return."

Came out 10 days ago, titled "COVID Tax Tip 2020-40: Here’s how much individuals will get from the Economic Impact Payments"