Yes thank you, to each age its book. Now we are living in the same age.
We have to see how Quran defines a Period (or Age).
When we look in to this in the light of whole Quran, we see every time a people's period comes to end, God reveals a new Book to guide them.
"To every [Ummah] people is a term appointed: when their term is reached, not an hour can they cause delay, nor (an hour) can they advance (it in anticipation)." Quran 7:34
According to this verse EVERY people (ummeh) has a period, therefore Ummeh of Islam also has a period.
Now the Question is how long was the Period of Ummeh of Islam. There are at least Two Hadithes, both indicates 1000 years:
The Prophet said, If my (Ummah) Community keeps on the right, it is going to enjoy an age of one day, and if it becomes corrupt, it will have an age of half a day. [Al-Munawī cites it in Fayd al-Qadīr from Shaykh Muhyī al-Dīn Ibn Arabī.]
If you are Sunni and you are not sure the above Hadth is Authentic, Here is a Sahih Hadith:
Volume 9, Book 93, Number 624: (Also in Volume 9, Book 93, Number 559)
Narrated Ibn 'Umar:
Allah's Apostle said, "Your stay (in this world) in comparison to the stay of the nations preceding you, is like the period between 'Asr prayer and the sun set (in comparison to a whole day). The people of the Torah were given the Torah and they acted on it till midday and then they were unable to carry on. And they were given (a reward equal to) one Qirat each. Then the people of the Gospel were given the Gospel and they acted on it till 'Asr Prayer and then they were unable to carry on, so they were given la reward equal to) one Qirat each. Then you were given the Qur'an and you acted on it till sunset, therefore you were given (a reward equal to) two Qirats each. On that, the people of the Scriptures said, 'These people (Muslims) did less work than we but they took a bigger reward.' Allah said (to them). 'Have I done any oppression to you as regards your rights?' They said, "No." Then Allah said, 'That is My Blessing which I grant to whomsoever I will.'
In Hadithes the 'relative' period of stay of people of Muhammad is explained in comparison to the duration of Christianity and Jews.
Muslims Period: equivalent to Afternoon till sunset
Christians period: equivalent to noon till afternoon
Jews Period: Equivalent to Sunset till noon
So, let's calculate Moslems period.
Christian period was about 600 years (From revelation of Jesus till Muhammad's)
Jews Period was about 1600 years (From Revelation of Moses till Jesus's)
Putting into equation:
sunrise till noon (Jews) = noon till afternoon (Christians) + afternoon till sunset (Muslims)
1600 years = 600 years + Period of stay of People of Muhammad
Period of Islam = 1600 - 600 = 1000 years.
I can't agree more to your second line
Let me ask you this: Why Muslims do not keep the Sabath Law?