I get why people are worried. I and most of the people I care about are in that upper age bracket and few of us in perfect health, but in light of the point made by other people I'm trying to imagine how we could make a lockdown with exceptions work.
All Emergency services of course would be exempt of course. (the military too)
All health workers including support staff in hospitals or elsewhere. That will include the receptionist at your GP and whoever cleans the place.
All workers involved in the production and supply of water, gas and electricity even down to the guy who checks for gas leaks and the ones digging up the road to do repairs.
Everyone involved in the production and supply of food. Shop staff, delivery drivers, wholesaler warehouse staff, all manufacturers of food including all farmers. We import food so the ships and docks must remain open.
Now make a list of all those above who have children and which schools they go to and which have relatives in care homes. Those schools and care homes must remain open for these people to work.
Add in all the public transport that the above people need and that must stay open too.
And now you have to take account of those teachers and public transport staff and where their kids go to school.
Oh wait. Not done yet. I assume people will be paying for food? They will need their salary/benefit cheques, so we have to keep open the banks and benefit offices and the admin people at the place you work.
Ah courts must go on and all the associated staff. They can't just stop.
And now we have to add to the list all the schools that their children go to and more care homes. It could even be 100% of schools by now.
I bet I forgot a lot of other essential people so feel free to extend the list.
I did! I forget rubbish collection.
Perhaps we should have stayed simple hunter gatherers