you touch on something I mentioned to some colleagues last week...... Rather than going full lockdown I wonder if it would have been better, to have simply gone lockdown for anyone over 60, or living with over 60 or with medical complications such as heart issues/diabetes etc.
the cost to the nation would have been less so this likley could have been brought in sooner. I am sure some would have said it was age discrimination etc and to those i would simply tell to shut up!.
hindsite 20:20 and all that
The goal of any mitigation plan is to limit the rate of transmission to something health care systems can manage. Pretty much everyone is going to be exposed sooner or later, but if everyone is exposed in a short period of time, many of those most in need of supportive treatment will never get it and death rates, as well as potential disruption to the rest of society and the economy, will be much more severe than it otherwise would be.
Anyway, if you want to limit the rate of infection, you have to target efforts at one group, those likely to be infected. It would be very hard to limit seniors' exposure by only targeting seniors. Even if you could justify limiting the movements of people based on age, targeting a small subset of the total population wouldn't do much to overall infection rates. Seniors would still get infected and would still die at nearly the same rates.