If the universe were infinitely old, it would have reached a state of entropy long ago. But, we are not in a state of entropy, therefore, the universe is not infinitely old and must have had a beginning. Because the universe has had a beginning it is not infinite in size. It would require an infinite amount of time to become infinite in size. Since the universe had a beginning, it has not had an infinite amount of time to expand, therefore it is finite in size.
All events have causes.
There cannot be an infinite regress of events because that would mean the universe were infinitely old. If it were infinitely old, the universe would be in a state of entropy, which it is not. If it were infinitely old, the universe would be infinitely large, which it is not. Since the universe is finite and had a beginning and there cannot be an infinite number of regressions of causes to bring it into existence, there must be a single uncaused cause of the universe. A single uncaused cause of the universe must be greater in size and duration than the universe it has brought into existence.