The apostles were eye witnesses to the events that occurred who later died despite the chance to recant what they were eyewitness to.
The date you give is a liberal one. It is almost certain that Luke, for instance, was written within 40 years, as we know Luke wrote Acts as well, and stopped that book around 61 AD, as Luke seems to have written without knowledge of St Paul’s martyrdom, but instead ends with him in chains. And Luke is not regarded as being the first written Gospel, either.
If you recall, Jesus died around 30 AD.