There are poor elderly people too. I think the best response in cases of true need like this is some sort of government intervention and rationing based on need as well as some sort of subsidy to make scaling production profitable. Politically the let the market decide ideology is utterly infeasible - not only are most politicians fundamentally good people that care about their constituents and simply aren't the type to stand by while there's a shortage, there's also the political consideration of how your relection chances will be impacted by attack ads detailing that time you stood by as an elderly individual saw a shelf stocked with purell but couldn't afford the gouged price who then went on to pass away due to the virus. Externalities might not be priced, but they can vote.

That's an inefficient proxy - there are plenty of poor elderly people (note that elderly people are often retired) and rich young people. If we're going to say anything other than "The people with the most ability to pay should get the goods because they have the most ability to pay, in and of itself," then the free market is the wrong tool to use.