I can't answer your question about age but since this is my favourite paper developer, I'm chipping in to say that I would be delighted if Ilford/Harman were to offer Bromophen once again in 1L packs like the one in your picture. Since the firm collapsed and then recovered, it's only been available in 5L packs. That means a lot of inconvenience and wastage for small-time users like me.
George, doesn't answer your request to Ilford for 1L pack but you might want to buy a Polypin box that holds 5L. Google it. It is like a winebox that holds 5L and dispenses the stock solution via a spigot. Very easy to use and doesn't allow air to penetrate the solution. Stock will last a long time in this box. You could also use 2 x 3L wineboxes once they are emptied and cleaned but more of a faff than a new 5L box