Referring to Matthew 21:19 and the fig tree as Israel being cursed for ever, the "for ever" here may not be intended to designate a length of time.  In some scripture "for ever" is used -- for lack of a better explanation -- as a kind of emphasis.  Rather than referring to length of time, "for ever" may simply be the judgment on the unbelieving nation of Israel that it be DEFINITELY set aside for such period of time until it would receive the Messiah.
 With regard to designation of length of time, the Greeks had no word designating everlasting or eternal as translated in the KJV.  The only way of ascertaining that the word meant "for ever" was from the context, and knowing that it was the only way they had to express the "eternal";  but the word "for ever" to which you refer means literally "unto the ages of the ages."  This is the same word or at least a derivative of the word that tells us hell is forever and our salvation is forever. But we know that "forever" in Matthew 21 does not imply an eternal curse because we have proof that Israel is not eternally set aside -- we have witnessed it's restoration, and comparing scripture with scripture, everything points toward Israel as one day being "life from the dead." (Romans 11:15)  But neither does "forever" imply "the end of the age" as you suggest.
  "Forever" may be used here to express the gravitas of Israel being set aside as a nation, although not ALL branches were "broken off" from the "root" only "SOME "(Romans 11) because there is a believing remnant through the church age,  It was, however, a hard sentence for the nation as a whole.
And in another sense, if "forever" here is translated as "eternal", it could mean an eternal curse on those within Israel responsible for her unbelief at the time.  Although Israel would be restored as a nation according to God's promises,  those unbelievers could never be restored, but were destined for hell.  They certainly would never bear any fruit again.
When Israel bears fruit again, it is of course a fulfillment of his covenant with them, but in truth it will be a resurrected nation, a "new creature" as the born from above are "new creatures" in Christ. "I will call them my people, which were not my people; and her beloved, which was not beloved." (Romans 9:25) It will be after they see the wounds in his hands and they                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                recognize Him as last, that the fig tree will truly bear fruit, after they have mourned for him tribe by tribe as one mourns for his only son. Zechariah 12:10  We will receive light on this as we are taught by the Holy Spirit.
In Yashuah,
Rachel