40 year old mission?

This article is in response to Marmzumah's article titled "The abysmal "revelations" of Mirza Qadiani"  I suggest reading that article before continuing on. In any case the jist of the article can  be taken from one quote from the article:

His mission was supposed to last forty years according to this prophecy, and at the time of writing (1892) he said that “ten full years have already passed” out of these forty. So his mission should last until 1922.

Mirza died in 1908.

The answer to this is:You have to read the whole text: "Now, let it be clear, that I was commanded, through a specific revelation, to call the people to Allah, in the fortieth year of my life, and I was given the glad tidings that I will live up to eighty years or thereabout. In view of this revelation, the tenure of my prophetic mission will extend to forty years out of which ten full years have already passed. (See page 238 of Brahin-e-Ahmadiyya)" The Promised Messiah (as) makes an incorrect estimate. The "specific revelation" he is talking about is in Barahin-e Ahmadiyya, pt. 3, which was written and published in the year 1882 AD/1299 AH. The Promised Messiah (as) was born in 1835 AD/1250 AH, which makes him 47/49 years of age at the time he got the revelation, not forty. Only because of this wrong estimation does he think that forty years are left of the revealed "eighty years or thereabout".  Nishan-e Asmani was written in 1892 AD/1309 AH. This means that "ten full years" is correct, both according to the solar calender, as well as according to the lunar calender. The Promised Messiah (as) died in 1908 AD/1326 AH. If you count from his date of birth until his date of death, he became 73/76 years of age. There is neither a revelation about him being forty years of age at the time of him being appointed to start to call people to Allah, nor about there being forty years left after the publication of Nishan-e Asmani. Both 73 and 76 are ages that can count as "eighty years or thereabout", but the second one is more accurate as one would expect revelations in an Islamic context to be attached to the Islamic calender system.