The entropy of a closed system never decreases, because closed systems spontaneously evolve toward thermodynamic equilibrium—the state of maximum entropy.
The above statement is known as the Second Law of Thermodynamics. In other words it states that the order of a closed system always decreases.
It is one of the basic principles of physics and indeed no process in nature has ever been observed where this law of nature does not apply. So if anybody comes up with a new theory that does not comply with this Law of Nature, it is considered false.
This law is one of the arguments why it is assumed that the age of the universe cannot be infinite. It must have had a beginning. Otherwise the universe would have reached a thermodynamic equilibrium yet, i.e. the entropy of the universe would have reached its maximum.
However this argument reverses the direction of the scientific method. It is unscientific to say that an observation is wrong, because it does not fit into one of our established laws of nature. If an observation and a law of nature are incompatible, then it is not the observation, which is false, but our law.
We can observe that the universe is not in a thermodynamic equilibrium. Therefore there must be a mechanism that decreases the entropy. Otherwise our universe would never have gotten into its current state. The assumption that the universe was in a state of minimum entropy at its beginning and has since increased its entropy doesn't explain how it got into such an improbable state in the first place. If there was no mechanism to reduce the entropy,the universe would have begun in thermodynamic equilibrium, because this is the most probable state. The probability that it started in such a highly ordered state with a minimum of entropy has an infinitely small probability and can therefore excluded as a possibility.
The Second Law of Thermodynamics is definitely false. At least it can only be valid under certain limited circumstances. Otherwise we could not explain the current state of the universe. If our universe and our laws of nature disagree, it is not the universe that is wrong. It is that we have the wrong laws.
Saying that the universe has only a limited age does not solve the problem, because we would have to explain how it got its initial state.
Therefore the Second Law of Thermodynamics is no valid argument for a limited age of the universe. Compliance wit this law is no argument at all, because we know for sure that this law has only limited validity. So we have to look where its limitations are. Which are the mechanisms that allow entropy to decrease? We know that they must exist, even if we don't know what they are. The Second Law of Thermodynamics can therefore not be used as an argument against a steady-state universe.