The older a building is, the more likely it is to be listed
SOURCE : ENGLISH HERITAGE WEBSITE
All buildings built before 1700 which survive in anything like their original condition are listed, as are most of those built between 1700 and 1840. The criteria become tighter with time, so that post-1945 buildings have to be exceptionally important to be listed. A building has normally to be over 30 years old to be eligible for listing.
Listing helps us acknowledge and understand our shared history. It marks and celebrates a building’s special architectural and historic interest, and also brings it under the consideration of the planning system so that some thought will be taken about its future.