Matthew 24:34 (and similar statements in Mark 13:30; and Luke 21:32) causes a lot of difficulty in the modern day. Jesus says "this generation will by no means pass away until all these things take place". This statement causes a number of problems. It is commonly picked up on by false teachers trying to capitalise on Eschatology, it is an attack point for atheists who want to try to say Jesus is 2,000 years late, and Christians who come across it in general reading wonder "what on earth does this mean?"
As usual, context is key. A vital question to ask is what exactly is meant by this generation? Whereas atheists will insist it refers to the generation to whom Jesus is speaking, the contextual evidence suggests otherwise. The three accounts militate strongly against this idea. Aside from the Matthew and Luke accounts saying no one knows when it will occur (Matthew 24:36; Mark 13:32), and Mark's account saying "let the reader understand" (v14), all three accounts include the analogy of a fig tree (Matthew 24:32; Mark 13:28; Luke 21:29). Jesus then says "when you see these things", and then comes the declaration that this generation will by no means pass away.
Thus, the generation that will not pass away before Jesus returns is not the generation to whom He was speaking, but the generation who observes the things of which He spoke. As yet, the things we are told to watch out for have not happened. Thus, the consistent message from Jesus is don't listen to anyone who says He's coming back now. Christians should not expect Jesus to come until these things come to pass.
Until these things come to pass, Jesus effectively says don't listen to anyone who says He's back, or that He's due to come back. As previously noted, Jesus said that no one, not even He (at the time He was speaking) knows. Therefore, His official message is to live as if He'll catch you off guard. As Christians, we need not concern ourselves with when Jesus is coming back. Tomorrow could be the start of all these things, or it could happen in many millennia. You could reach the end of your own life, and Jesus may still say "just one more person... I want to wait until just one more person comes to faith", and He can do that again and again and again. Another 6,000 years could pass from now until then, and there's no scripture to say otherwise. But more importantly, you may still be alive. What would you rather be doing in that day? Preparing for it, or slacking off?