How is this a problem that needs preventing? Alternate title: "People like living in the city more these days"
I don't think it's good for the social makeup of small towns and villages. Healthy communities need people of all ages, not just retirees.
[1] this is kinda possible in a city, but usually costs a fortune. I used to live near allotments in Edinburgh but they were super expensive to rent.
Most second tier cities aren't as close to a major city as oakland is to SF, but you can find what you are looking for if you are willing to live the slightly less cosmopolitan life of SF/LA/Chi/NYC/DC/etc.
Of course, I have no idea how this translate to the UK!