There is no evidence to suggest that any of the gospels were written by eye witnesses of the events described in them. Keep in mind that all the Gospel required apostolic authorship in order to be accepted into the Bible and this played a large role in how these Gospel came to be seen.
When you consider the Gospels, it is very important to understand how they were composed in the first place.
The Gospel of Mark was composed first between 65-80 CE. The church father Eusebius (late 3rd century CE) is the earliest surviving record in regards to the claim that the Gospel of Mark was written by Mark, a Greek translator and follower of Peter. He quotes from Papias who lived in the early 1st century BCE who said that the book was written after Peter had died and that Mark "wrote down accurately whatsoever he remembered". It was not, however, in exact order that he related the sayings or deeds of Christ. For he neither heard the Lord nor accompanied Him." Thus Eusebius himself quotes that Papias stated that this Mark had never met or seen Jesus himself, i.e. he was not eye witness.
What makes this claim more questionable is the fact that Papias himself was known to exaggerate when it came to his historical claims. When describing Judas' last days he says that Judas became so bloated that his head was wider than a wagon. We also have to remember that none of the gospels originally had any titles and titles such as "The Gospel of Mark" were only added by scribes much later on. For instance Papias mentions the Gospel of Matthew and only describes it as a collection of Jesus' sayings. The Gospel of Matthew contains much more than just the sayings of Jesus and it leaves one wondering if Papias might have been referring to a different gospel all together. You can find more information on the Gospel of Mark here.
The Gospel of Matthew came to us as being anonymous but through church tradition, the apostle Matthew became the recognised author. Later on the Gospel was edited with the text stating that this was the Gospel of Matthew. This however is only church legend and the author was not an eye witness himself.The Gospel was most probably written between 70 CE (after the fall of Jerusalem) and before 110 CE when Ignatius quotes from it.
Nowhere in the Gospel of Luke does it state that Luke the apostle was the author, however this had become accepted church tradition by the late 2nd century. The author is the same author as that of Acts. The author also never states that he is an eye witness at all but that he did a significant amount of research before writing his book (Luke 1:1-4). The Gospel itself is difficult to date but it was most probably written towards the end of the 1st century CE. If Luke relied on on the Jewish historian Josephus, then the gospel could have been written as late as 93CE.
Both Matthew and Luke used Mark as the source for their gospels in addition to another gospel called Q, which was essentially a collection of Jesus' sayings. Both Matthew and Luke used Mark as the source for their narrative and Q for their source for Jesus' sayings. Why would a real eye witness rely on Mark for most of his narrative? Mark was not even an eye witness himself? Why would they need to rely on a sayings gospel when they were there to hear the words for themselves? One could use the argument of old age but by this time your whole theory of the validity of eye witnesses is thrown out of the window.
So we now know that neither Matthew, Mark or Luke were eye witnesses but based their gospels on older sources. This then leads us to the Gospel of John.
John is unique in that it does not rely on Mark at all. It was written much later than the other gospels, probably around 90 AD, which would make any disciple at least 80 years old. What makes the dating for this gospel difficult is that it seems to have been heavily edited. The first chapter for instance uses a very different style of Greek than most of the rest. When some of Jesus' miracles are mentioned, the Greek once again reverts back to the style from the first chapter. This indicates that later additions were made to the text. The author once again does not claim to be an eye witness himself. Some evidence within the Gospel strongly suggest that the author was not an eye witness, for instance he keeps referring to Christians being expelled from the Jewish Synagogues. Any eye witness (or reader of the other gospels) would have known that Jesus himself often taught in the synagogues.
Thus we are left with virtually no evidence that any of the gospels' writers ever witnessed the life of Jesus and cannot be considered as eye witness accounts.