Saint Andrew is listed as one of the twelve apostles of Jesus Christ, however on Wikipedia, it is written that Saint Andrew was born in 5 BC. How is it possible that a 5 year old child is an apostle? In the painting of The Last Supper, there is no sight of a 5 year old child.
1 AD represents Jesus' birth, not his ministry or death & resurrection
The Anno Domini method of numbering years was devised by Dionysius Exiguus in which he said that the current year was both "the consulship of Probus Junior" and 525 years "since the incarnation [i.e. the birth] of our Lord Jesus Christ". It's not clear how he came to that reckoning, but it's clear that Jesus' birth was estimated to be at 1 AD (or alternatively, 1 BC). Since Jesus is traditionally said to have died at 33 years of age, Dionysius' reckoning would place the Last Supper at around 33 AD when St. Andrew would have been 38 years old.
The exact date of birth of Jesus is a large enough topic to warrant its own Wikipedia page, but modern scholars agree that his date of birth was between 6 BC and 4 BC (several years earlier than Dionysius' estimates). Again, that does not make it unfathomable for Saint Andrew to be called as a disciple, since he would be about the same age as Jesus.