"When Jesus explains the signs of the last days, he refers to the fig tree and says that the generation that sees these signs and the restoration of Israel shall not pass away: How long is a biblical generation?"
This question is answered incorrectly by many Bible "scholars." They look at a generation in terms of a concrete, one-time number fitting every generation, which is not applicable to every generation. For example, Adams generation lived longer than our modern-day generation by several hundred years. One scholar tried to whittle down a generation by taking the average and came up with 53.3 years or somewhere near that time, which is foolishness. The answer is that it depends at which generation the "fulness of time" takes place.
An interesting definition given in scripture for determining a generation is Deut 1:39 which states, "Moreover your little ones, which ye said should be a prey, and your children, which in that day had no knowledge between good and evil, they shall go in thither, and unto them will I give it, and they shall possess it." This scripture defines one, full generation of Israelites who were not allowed to enter the Promised Land after they were delivered from Egypt because of their sin. Why is this scripture so important in determining the definition of the generation at the time when the Lord returns? The scripture defines the generation not allowed to enter the Promised Land starting from those children who knew the difference between good and evil. What age is that? That depends on the child but normally is between 4 -- 7 years old. No one can prove that, however it is a good estimate. Anyone before that time was not allowed to enter Canaan. If you add the numbers then defining a generation as an amount of time is not correct. Why, because that generation lasted 40 years, the time the nation of Israel wandered in the desert. One full generation in the Bible does not equal 40 years no matter about whose generation you are speaking. There are actually 7 definitions for the word generation. Which definition is the Lord using when He said, "This generation shall not pass, till all these things be fulfilled."
One definition says a generation is all of the offspring that are at the same stage of descent from a common ancestor. Another definition says the average interval of time between the birth of parents and the birth of their offspring equals one generation. Most people think of a generation as the latter definition. If one uses that definition than no single time frame for a generation will fit prophecy because some generations last longer than others. The definition which fits prophecy states all of the offspring as the same descent from a common ancestor. This brings up the question of where does one generation start and where does the other generation end? That cannot be answered unless a definite starting point for a generation is determined. Jesus names in this prophecy the starting point of the generation that witnesses "the blooming fig tree." The last generation may last 60, 70, 80, 100, plus and no one knows. However, you can know the starting point of the last generation. One can safely conclude from that starting point there is only going to be 60-100 years left depending on when the last of that generation dies off.
However, when did the last generation start. Many people claim it started in 1948 when Israel became a nation. If that is true, and those who could determine between good and evil (4-7 year olds) witnessed the birth of Israel, then that generation of people would be around 64-67 years old today (2008) and could be dying off in the next 10-20 years. That would be 2018 to 2028 AD. That really makes sense since many people claim the Church Age is 2008 years old and should have expected the Lord to return around 2000 AD (and did not). However, they skip one most important fact. That time period they use begins with the birth of Christ and not the crucifixion and resurrection in 33 AD which is the true start of the Church Age. They are off by 33 years. If one counts the Millennial Reign of Christ beginning in the 7th Millennium, then they need to get the starting point of the 7th Millennium correct. That is 2000 years after the resurrection of our Lord and the beginning of the Church Age and ending in 2033 AD. Now, subtract 7 years for the time of Jacobs Troubles, the point where the Christians will be raptured out of this world to meet the Lord in the air. The numbers come out to 2026 AD. That is just about the time this last generation is going to die off. Once you start seeing Solomon's Temple being rebuilt (once the Dome of the Rock is destroyed), and the Temple sacrifices started up again, then you know the fig tree is in full bloom!
...lift up your heads; for your redemption draweth nigh. Be ye also patient; stablish your hearts: for the coming of the Lord draweth nigh.