Although Thomas Aquinas' logic in the above example was dreadful, Aristotle did a little better; as izubachi points out, when the argument for a first cause is phrased as shown above, (IV) does not follow on from (III).
Aristotle however, came up with quite possibly the most hilarious, most brilliant philosophical concept EVER in proof of (IV). He stated that the Universe could NOT be of an infinite age, because we would have never reached the present day if that was so...
I laughed for about ten minutes after I heard this. Not disputing it (...necessarily; I leave that to greater minds than mine), but just utterly amused by the whole idea!