That is actually not entirely true. The universe may be 13.8 billion years old from our perspective. You know of course that gravity affects the passage of time. When you are close to objects with large mass time passes slower. The bigger the mass the slower time passes. When the big bang happened the mass of the whole universe was in the same exact spot, and we don't even know how much mass there is on the universe. With that in mind it is very possible that from a general perspective and not our perspective the universe is actually infinite years old.
