We're accustomed to framing timing issues in early Christianity around Jesus' life. He died in the 30s, so we think of a document written in the 60s as postdating Jesus' life by about three decades, for example.
But we need to keep in mind that many significant events, like the ones narrated in Acts, occurred after Jesus' life on earth. Acts closes with events in Rome in the 60s. Some people who were in Rome at the time surely lived into the second century, probably multiple decades into the second century in some cases. That diminishes the popular skeptical suggestion that individuals in the second century wouldn't have had firsthand knowledge about issues like the dating and authorship of documents, were just speculating about such issues without much to go by, etc.
I've cited Acts as an example here, and something else that's significant about Acts is its connection to the third gospel. The fact that people with firsthand knowledge of Acts' authorship and the circumstances surrounding it could so easily have lived well into the second century, and that some probably did, adds weight to the universal testimony from the second century onward that the third gospel was written by Luke. (And there are multiple sources who partially or fully corroborate that authorship attribution prior to Irenaeus, as discussed here.)
This distinction between the timing of Jesus' life and the timing of later events is also relevant in many other contexts: the suffering of the apostles, their martyrdom, apostolic miracles, etc. Always ask yourself what timeframe is relevant to the issue under consideration. Be careful not to assume the timeframe of Jesus' life in contexts that involve a different timeframe instead.
