Because there are not enough tests to test everyone, it is impossible to say how widespread the virus really is, how it is transmitted, and how deadly it really is. Therefore, the only rational way to limit the spread is to apply social distancing principles to EVERYONE worldwide. I personally hate some of the ridiculous practices that are being implemented here in my home area in the US (one grocery chain is spraying incoming customers with hand sanitizer) but it is what it is. I don't think only isolating/quarantining older people will work well enough.