When I was about to enter college with Civil Engineering course, a Polo Barong vendor told me that when I graduate there will be no more place to build and I will end up unemployed. Then I told her, "Ako mag-aayos ng mga ginawang structure ngayon (I will repair structures build today)."
Indeed.
As technology advances, structure existing today can last a lifetime when properly treated from time to time. Concrete or masonry cracking can signify deficiency and must undergo investigation. Corrosion has no place in steel structure and must be treated immediately to avoid decrease in member section. Timber is a dwelling place for fungi, termite, boring insect, and bacteria.
The life span of a structure can vary, depending on the maintenance and monitoring the owner provides.